Chapter II

) which are endowed with the most pronounced activity and which play the principal role among the blood cells or phagocytes. That phagocytosis plays a most important

## part in the inflammatory process is a matter to be emphasized in more

than one way and in more than one place. The account of the process already given should suffice for descriptive purposes; the importance of the act, however, should be made most prominent in considering inflammation and suppuration. That the phagocytic properties of these cells are limited will be remembered when we recall that in certain instances phagocytes, which are incapable of defence as against the mature bacterial organism, are yet capable of englobing the spores and preventing their development. Nevertheless, the activities of even the most lively phagocytes are capable of being influenced and repressed by extremes of heat and cold to which patients may be exposed, either locally or generally.

CHEMOTAXIS AND OPSONINS.

Having considered briefly the cells which take prominent part in the inflammatory process, and the escape along with them of the fluid portions of the blood, whether these coagulate or not, it is necessary before referring to specific factors to discuss that which induces the above cells to act in this way. That there is a peculiar, even a mysterious, attraction which brings specific irritant and phagocyte together has been for some time recognized, but it remained for Pfeffer to study it carefully and to give it the name by which it now passes, _i. e._, _chemotaxis_, while others have widened our knowledge of it, especially by a recognition of the _opsonins_ or material which “prepares food,” _i. e._, prepare microbes for ingestion by the phagocytes.

Chemotaxis is a term implying a peculiar property of _attraction and repulsion between cells_, both animal and vegetable. It mainly pertains to vegetable cells alone, and has been offered as the explanation of the sporulation of ferns, for example; but as it interests us most in this place it is manifested between the animal cells of the human body and the bacteria, which are vegetable cells. As a result the former, _i. e._, the phagocytes, having power of migration, are drawn toward the latter. To be more accurate, this mutual or peculiar attraction is known as _positive chemotaxis_, it being also known that exactly the reverse prevails under certain circumstances, and that mobile cells will move away as rapidly as possible from certain organisms or substances for which they seem to have a repugnance, this being known as _negative chemotaxis_.

SPECIFIC IRRITANTS.

These are essentially living organisms, bacteria, fungi, and the protozoa, the first named being by far the most frequent. Before a lesion can assume the type of inflammation as here understood some one or more of these organisms must have secured an entrance into the tissues, the circumstances determining such invasion being considered a little farther on. It is these living organisms which, having once invaded the tissues, determine that most active congregation and proliferation of certain cells which we have just described under the head of Phagocytosis. When once the irritants are present there begins that very active conflict which Virchow has so graphically alluded to as the _battle of the cells_. Now the mysterious chemotactic properties of the component substances manifest themselves, and now phagocyte is drawn toward bacterium, or the reverse, while the tiny war goes on with sometimes varying results, it being a question which can prove victor in the conquest. This is no fiction of the imagination, but is a contest which may be seen under the microscope in certain of the lower animals, while its results may be seen in the examination of pus from any human source. In another place I have also likened this conflict to that in which certain of the enemy resort to poisoned weapons, because modern biological chemistry has now shown very evidently that it is a part of the life history of many of these microörganisms to produce, probably as excretory products, albuminoid or other substances having sometimes extremely toxic properties. And so it comes about that in many of the surgical infections, while the local destruction is produced by the actual death of tissues which have been invaded by microörganisms, the general or systemic symptoms, generally referred to as the _toxic_ symptoms, are literally due to poisons generated in the infected area, dispersed throughout the system, and often proving fatal.

The _local effect of these specific irritants_, when they are not promptly attacked, devoured, and removed by phagocytes, is _pus_, which means cellular death, or gangrene, which is death of masses of cells which have not had time to separate from each other. Pus, then, is the ordinary consequence of the contest above alluded to, and _each pus cell represents the dead body of a phagocyte_ which has perished in the attempt to protect the parent organism from harm. That it has died valiantly can almost invariably be determined, because within its dead body may be seen one or more of the minute invaders which it has attacked. This, then, is the light in which inflammation and infection should be viewed.

In other words, we may have escape of fluid portions of the blood, which may or may not coagulate; we may even have some escape of corpuscular elements with some activity in the extravascular cells, which shall lead to temporary or even permanent enlargement of a part; all of which may be provoked by injury or by the presence of certain chemical irritants within the blood or tissues; for example, alcohol, uric acid, etc. But the factors which provoke the greatest activity on the part of intravascular and extravascular cells, and which determine the richness in albumin of fluid exudates, or their prompt coagulation as soon as blood serum has escaped from the vessels, and which

## particularly determine the furious rush of phagocytes and that kind

of intercellular conflict which leads many of the contestants on both sides to death, are living organisms which are introduced from without, whose presence at the point of inflammation is abnormal and injurious, which are offending substances in every respect, while the whole phenomenon of inflammation is an expression of an effort to rid the system thereof. Taking this view of the subject, there is an important distinction between hyperemia and its consequences, which is absolutely a non-infectious condition, and inflammation with its consequences, which is always an infection and is always followed by more or less death of cells, the same being often extruded in a semifluid mass known as _pus_.

CIRCUMSTANCES WHICH FAVOR INFECTION.

1. =The Virulence of the Infecting Organisms and the Amount Introduced.=--There is the widest difference between various forms of microörganisms in the matter of virulence; and it is true that there are very great differences between the same species under different circumstances, these differences depending on conditions as yet absolutely unknown. With certain organisms it is enough to infect an animal with one alone in order to bring about a fatal result, this meaning that the organism itself is extremely virulent and the animal extremely susceptible.

In a guinea-pig, for instance, a single virulent anthrax bacillus will produce death, whereas in a more resistant animal many are required, and in still others there is absolute immunity against the disease. Man is much more susceptible to the pyogenic organisms than most of the lower animals, which is one reason why wrong deductions have been drawn from many experiments, and why veterinary surgeons, who are so careless of all antiseptic precautions, as a rule have good results in work which, done after the same fashion on the human being, would be inevitably fatal. It is one reason also why one may draw false inferences from experimental work, for instance, upon dogs, which survive many an operation which can scarcely be successfully repeated upon a human being. The influences which affect the vitality and virulence of microörganisms are most numerous and widespread. Temperature, sunlight, moisture or dryness, association with other bacteria, are but a few of the conditions known to be more or less operative. Inoculation with a small number of certain bacteria may be harmless; up to a certain number it may produce only a local disturbance, like abscess, while a still larger dosage may produce fatal results. This is not the case with all, however, but only with some organisms. Bacteria which have been repeatedly passed through the animal body become more virulent than those cultivated for many generations in test-tubes in the laboratory. This variable virulence is especially characteristic of the colon bacillus, the anthrax bacillus, and the micrococcus of erysipelas. Nor does it always follow that the most virulent organism is necessarily cultivated from the most toxic or serous manifestation of its activity.

2. =Association.=--Bacteria are seldom found in pure cultures under natural conditions. By mutual association remarkable changes are produced, sometimes in the direction of enhanced virulence, sometimes in the direction of attenuation of effect. Certain organisms, extremely dangerous alone, lose their power when combined with others, while still others have their virulence increased to a rapidly fatal degree. In fact, these effects are so strange and so contradictory that no law governing them has yet been formulated, it being necessary to establish each case by experimental investigation. The virulence of the anthrax bacillus under ordinary circumstances is well known, as is also that of the streptococcus of erysipelas in man. Yet, when these two organisms are introduced simultaneously, the mixture is apparently wellnigh harmless. On the other hand, the simultaneous inoculation of certain other species greatly increases the danger from either alone. The diplococcus pneumoniæ when combined with the anthrax bacillus seems to have a greatly augmented power.

3. =Hereditary Influences.=--The fact that immunity against certain infections and susceptibility to other conditions are transmitted from parent to offspring is one which admits of no dispute. The explanation, however, is almost as remote from us today as it ever was. But the recognition of the fact is of the greatest importance to all practising surgeons. That bacteria frequently enter through wounds and bruises is self-evident, but we all know that such wounds are more likely to suppurate in some than in others, and the causes of infection in some are, to a certain extent, connected with the hereditary habit of tissues. The same causes influence not merely liability to infection, but its severity and character. There are undoubtedly also local as well as general variations, and it is very certain that among these the results of bruising or contusion are by far the most prominent. There is also undoubted experimental evidence that under certain circumstances bacteria produce only local lesions, whereas under others they produce general and even fatal infection.

4. =Local Predisposition.=--Local predisposition is a factor of almost equal importance. Once given a distinct infection, and hyperemia is sometimes a contributing cause of inflammation. _Per contra_, anemia of tissues seems to be also a favoring condition. In parts involved in chronic congestion the blood flows more slowly, while the vessels are dilated and apparently susceptibility is increased. Infection here produces a type of disease mentioned as _hypostatic inflammation_. Conspicuous exception as to the occasional value of an artificial passive hyperemia is seen, however, in the so-called congestion treatment (Bier’s) of tuberculous joints, where the more or less constant flooding of the tissues with venous blood seems to render them uninhabitable for living bacilli, which apparently die and disappear (by phagocytosis), thus permitting a slow return to the normal condition. General anemia, again, is a predisposing cause, while toxemias, including diabetes, etc., are still more so. The liability of diabetic patients to suppurative and even gangrenous infection is proverbial. The presence of foreign bodies has much to do also, and, infection once having occurred along with its introduction, the presence of a foreign body will nearly always excite suppuration; otherwise it will ordinarily remain inert. The withdrawal of trophic nerve influences also apparently permits infection, as is instanced by the ease with which bed-sores form in paralytic patients. Obstruction to the circulation or to escape of secretions more easily permits infection; for example, in the appendix, in the kidney, in the gall-bladder, the salivary glands, etc. Furthermore, one may formulate a quite comprehensive statement and say that all such lesions as solutions of continuity, hemorrhages, degenerations, vascular stasis produced by strangulation, etc., and all perforations, increase more or less the liability to infection.

5. =Pre-existing Disease.=--Here are reckoned, first, _previous and long existent toxemias_, _e. g._, syphilis, diabetes, scurvy, etc. Other conditions, like lithemia, cholemia, acetonemia, and the various conditions represented by oxaluria, or in which acetone, peptone, and excess of uric acid are found in the urine, also come under this head. One need never be surprised to find suppuration occurring in those cases in spite of due observance of all ordinary precautions, since by their existence immunity is destroyed and vulnerability increased. (See chapter on Auto-infections.)

_Recent toxemias_ also have important bearing in this same respect. For instance, after typhoid fever and other acute wasting diseases, including the exanthemas, surgical operations are sometimes followed by failure, and should always be postponed until complete recovery, except in cases of emergency. The condition to be hereafter described as _enterosepsis_, and which has previously been known under many different names, as fecal anemia, stercoremia, etc., is one which makes the performance of all operations dangerous, and which certainly predisposes to septic disturbances of all kinds. The postpuerperal state is also one in which operations are to be avoided if possible.

Certain _anatomical changes peculiar to the various ages_ also belong in this category. Old age, with its accompanying arterial sclerosis, its cardiac debility, and other well-known tissue alterations, favors sluggishness of wound repair and leads not infrequently to sloughing or to bed-sores. Amyloid changes betoken impaired vitality. Children are much more liable to acute osteomyelitis than adults. Nursing infants are apparently exempt from many of the infectious diseases, but possess relatively small power of vital resistance to surgical operations. General anemia and impaired nutrition of the body predispose to most infections and to acute starvation.

6. =Personal Habits and Environment.=--_Diet_ has much to do with tissue resistance. Rats fed on bread are more susceptible to anthrax than those fed on meat. Hunger makes pigeons highly susceptible to the same disease, and artificial immunity induced in various animals is quickly destroyed by starvation. Prolonged thirst seems to have the same result. Excessive fatigue generally reduces immunity, as already mentioned. The various drugs which destroy red corpuscles impair immunity, and even by injection of water into the circulation the bactericidal power of the blood is reduced. White mice fed with phloridzin, which produces artificial diabetes, become highly susceptible to glanders, from which they are ordinarily exempt. In this connection may also be mentioned the various toxemias alluded to under the previous heading, which may proceed from the intestine, from the genito-urinary tract, and probably also from other sources. Climate has more or less to do, as also extremes of weather, with power to resist infection or to survive serious operations. Dark habitations, poorly ventilated, constitute surroundings which manifestly predispose to infection of all kinds. Rabbits inoculated with tuberculosis and confined within a dark cell, badly ventilated, become rapidly diseased, while others similarly inoculated, but allowed to roam at large, present but slight evidences of the affection. Certain occupations predispose to certain diseases. This is pre-eminently the case, for example, with workers in mother-of-pearl, who are exceedingly liable to a particular form of osteomyelitis; and with those who make phosphorus matches, who are prone to suffer from a peculiar necrosis of the lower jaw. Prolonged suppuration may produce such changes in the blood and tissues that vital processes of repair, cell resistance, and chemotaxis may be so far interfered with as to facilitate subsequent infection.

Finally, the _influence of local injury to tissues_, particularly of contusions which cause tissues to lose their vitality, is strenuously insisted upon by all, and is spoken of repeatedly in other places in this work. Many tissues will succumb to inoculation after bruising, ligature _en masse_, etc., which before such injury are not in the least disturbed.

7. =Fetal Infection.=--It is only in a very limited class of cases that infection can be transmitted from mother to fetus, but there are instances of this kind in which the surgeon is deeply concerned. As Welch has stated, syphilis is the only infection capable of direct transmission through the ovum or spermatozoön; but intra-uterine infection may occur in many ways, and many diseases may be thus transmitted. The placenta is usually regarded as a perfect filter; nevertheless, it is occasionally passable to microörganisms. These may be caused by preëxisting lesions in the placenta or by the virulence and activity of bacteria. It is known that in animals the bacilli of chicken cholera (inoculated into the mammalia), of symptomatic anthrax, and the pyogenic cocci, frequently traverse this barrier. In mankind infection _in utero_ has been observed in smallpox, measles, scarlatina, relapsing fever, syphilis, tuberculosis, croupous pneumonia, typhoid fever, anthrax, and surgical sepsis.

SOURCES OF INFECTION.

That the effects of bacterial invasion may be anticipated and guarded against most effectually it is necessary that the practitioner should be thoroughly familiar with the sources from which they come, and the localities in and about the body which they most commonly inhabit or where they are met with in largest numbers.

=Skin and Mucous Membranes.=--Of all possible sources of infection, the skin itself is probably the most fertile. It is exposed to contamination by air and by everything which may come in contact with the body, and there is perhaps no organism met with in disease which may not be found upon its surface or within its recesses. In fact, these recesses, such as the crevices beneath the nails, the spaces between the toes, and the various pockets like the tonsils, the axillæ, etc., are those most commonly inhabited by microörganisms.

Bacteria may penetrate the skin by means of three different routes, namely, the sweat glands, the hair follicles, and the sebaceous glands, by means of their regular openings. The hairy appendages of the skin are even greater sources of danger than the skin itself, since a direct path of infection into the depths of the skin is afforded by their follicles. Experimentally it has been shown that when bacteria are rubbed into the skin where there are no follicles, there is freedom from infection, whereas the reverse is equally true, and it is clinically generally recognized that furuncles and carbuncles form almost exclusively in those parts provided with hair and sebaceous glands.

The mucous membranes are in constant contact with microörganisms and furnish conditions in many respects favorable for their rapid development. Nevertheless, the latter is interfered with and often inhibited by certain mechanical and chemical influences which afford protection. The conjunctiva is an extremely exposed membrane, which harbors, however, but a relatively small number of bacteria under ordinary circumstances. The tears before escaping from the conjunctival sac are sterile, and are probably saline enough to act as an antiseptic bath for the cornea. Moreover, by free escape of secretion through the nasal duct the conjunctival sac is kept constantly irrigated, to which is mainly due its ordinary healthy condition, as it is well known how commonly lesions follow obstruction to the lacrymal duct. The horrible results of Egyptian ophthalmia, _i. e._, the pyogenic form of conjunctivitis, are familiar to travellers in Egypt. Howe and others have shown that this disturbance is due to flies, which are carriers of infection, and are attracted toward the eyes of infants, while the superstitious notions of the parents restrain their children from instinctive protection of the eyes when thus irritated. There is probably no greater common carrier of pyogenic infection than the common house-fly, and nowhere is this agency more demonstrated than in the hot climates of the Orient.

[Illustration: PLATE III

FIG. 1

Artificial Dental Caries in Cross-section. Tubules Filled with Bacteria. (Miller.)

FIG. 2

Putrid Tooth Pulp. Infection of Dental Tissue. × 1000. (Miller.)

FIG. 3

Dental Caries. Disappearance of Dental Tissues as Result of Presence of Bacteria. (Miller.)

FIG. 4

Dental Caries. Tubule Filled with Cocci. (Miller.)

FIG. 5

Dental Caries. × 500. (Miller.)

FIG. 6

Dental Caries. Tubules Plugged with Cocci. × 500. (Miller.)]

=Upper Respiratory Tract.=--The oral cavity and pharynx are seldom free from bacteria. Miller has studied over one hundred species that he has found under various circumstances in the human mouth. Some of these are pathogenic; others are apparently absolutely innocent. Many of the forms which grow in saliva will not grow in ordinary media. (See Plate III, illustrating infection of the teeth.) Miller has also shown that many forms of dental caries are but expressions of bacterial invasion even of those apparently most solid structures, the teeth; and of late we have been taught more fully that such invasion may extend far beyond the confines of the teeth alone, and may spread to various, even to distant parts, and produce possibly fatal mischief. Abscesses in the brain and extensive septic infections have been traced to invasion along the line of the dental tubules. One of the most virulent of all the common inhabitants of the mouth is the pneumococcus of Fränkel, known also as the micrococcus lanceolatus of Stebernrg. In virulence it is a variable organism, but it is present in a virulent state in only 12 or 15 per cent. of cases of infection due to it. This is the organism which is the cause of lobar pneumonia, and frequently of bronchopneumonia, as well as of numerous phlegmons and other inflammations of the throat, and which, getting into the general circulation through the tonsils or other possible ports of entry about the mouth, causes serious septic and inflammatory disturbances in widely distant regions. Aside from dental caries, a widely opened port of entry is often afforded by those ulcerations around the margins of the gums which are produced by accumulations of tartar. Disease in the antrum of Highmore, for instance, and many other local destructions, are frequently caused in this way.

The next most common port of entry is the _tonsils_, faucial, lingual, and pharyngeal, which contain a variety of crypts which are often filled with secretions or retentions loaded with bacteria. One of the most common sources of an involvement of the cervical lymph nodes in tuberculous disease is an infection springing first from the tonsils or the teeth.

In spite of the fact that myriads of bacteria are swept into the nasal cavities with the air we breathe, few are seen in the nose. A peculiar capsule bacillus, closely allied to that described by Friedländer, has been found in a number of cases of ozena, while the pneumococcus of Fränkel is also often found there, and is known to produce abscesses of the brain. One specific organism--namely, that of _rhinoscleroma_--concerns the nose almost solely, its first ravages being met with in this location.

=Alimentary Canal.=--Probably more microörganisms enter the alimentary canal than gain access in any other way, these coming both from food and drink as well as air. Once within its confines, few of them are capable of prolonged existence. Welch states that the meconium of newborn infants is sterile, but that within twenty-four hours it usually contains abundant bacteria. That bacterial infection through this passage-way is a fertile source of non-surgical lesions is well known. The possibility of surgical infections being produced in the same way is both more remote and less demonstrable. Naturally, anaërobic organisms find here more favorable conditions, and even extremely acid or extremely alkaline conditions do not serve to destroy all such life. Pyogenic cocci are often present and are frequently found in peritoneal exudates. In the intestines of herbivorous animals the tetanus bacilli and those of malignant edema are regularly found. The fungus of actinomycosis also finds its way into the bowel along with ingested food. Under ordinary conditions the bile in its natural reservoirs is free from bacteria, but the colon bacilli and pyogenic cocci often invade these precincts.

=Genito-urinary Tract.=--Even the healthy urethra may contain bacteria. While these may wander upward to an indefinite extent, it is believed that the urine contained within the bladder in a condition of perfect health is free from bacteria, and that if such gain entrance they do not long remain. The same is true of the female bladder and urethra. The vagina contains organisms of many species, some of which do not grow on ordinary culture media, but are to be recognized by the microscope. While it is generally acknowledged that the vaginal secretion is, as a rule, possessed of bactericidal properties, there is as yet no satisfactory nor comprehensive explanation of this fact, its normal acidity not being sufficient to account for the fact.

=The Milk in the Lacteal Ducts.=--In a condition of perfect health milk secreted from the ideal mammary gland is sterile, but may easily become contaminated upon its exit from the nipple. Conversely, under many favoring conditions organisms may travel into the lacteal ducts from the skin without, and thus contaminate the milk. In all probability the breast corresponds in behavior to other glands whose ducts open upon the surface, and, while such openings invite entrance of bacteria, their migrations do not extend far from the surface unless some of the other conditions already mentioned predispose to further infection or extension.

In summarizing the general topic of possible _sources_ and _paths of infection_ bacteria may enter and exert deleterious action:

A. _From within the system_; and

B. _From without_.

A. _From within_ they may enter the tissues either through the inspired air, through food and drink, _i. e._, ingesta, or by means of more direct inoculation, _e. g._, by foreign bodies or by venereal contact. The danger through infection by inspired air is very small, and concerns probably a limited number of organisms, of which the tubercle bacillus is the most important. Foul air and air which emanates from sewers, cesspools, etc., while most unpleasant to breathe and deleterious in many other ways, do not necessarily contain any microörganisms which can be injurious. This fact, in opposition to general belief, is, nevertheless, proved by recent investigations. The ingesta furnish the most fertile source of contagion from within, but the diseases thereby produced fall for the most part into the domain of medicine rather than that of surgery.

B. _Infection from without_ the body may come by actual contact with previous skin or mucous lesions, and particularly from noxious insects and certain parasites. Among surgeons the principal sources of contact infection to be enumerated and guarded against are:

1. Skin and hair;

2. Instruments;

3. Sponges or their substitutes;

4. Suture materials;

5. The hands of the surgeon and his assistants;

6. Drainage materials;

7. Dressing materials;

8. From miscellaneous sources, _e. g._, drops of perspiration, unclean irrigator nozzle, a contaminated nail-brush, the clothing of the operator, etc.

While insisting here upon the recognition of these sources of danger, the precautions to be taken against them are to be considered under another heading, to which the reader is referred.

One of the greatest sources of possible infection has of late been shown to be the presence of flies and other noxious insects, which act as carriers of infection. The Egyptian ophthalmia, which ruins the sight of 30 per cent. of the inhabitants of Egypt, has been shown by Howe and others to be due to infection by this mechanism; and a simple bacteriological experiment will suffice to show that the foot-tracks of a single fly across a wound furnish abundant opportunities for infection with organisms which are presumably virulent. In fact, the danger of carriage of infection by this means is greater than from almost all other sources, except the use of improper materials during surgical operations.

CLASSIFICATION OF INFECTIONS.

We speak of infections as _primary_, _secondary_, and _mixed_; and it is necessary, for purposes of accuracy at least, to make a reasonably clear distinction between them.

=Primary Infection.=--By primary infection is meant infection with a single form of organism whose effects are prompt and speedy. Of this, erysipelas or syphilis may serve as illustrations. Most of the acute infections belong to the primary type.

=Secondary Infection.=--Secondary infection means that after certain disturbances due to a primary infection, _i. e._, one of a given type, there occurs at some later period and from a distinct source another infection whose results may be more or less disastrous, and cause the case, at least for the time being, to assume a different aspect. We have an illustration of this in the case, for example, of primary tuberculosis with distinct infection of a number of lymph nodes, which, acting as filters, have caught in their tissue net a large number of tubercle bacilli that, lodging there, have produced the usual well-known results and have practically converted the infected nodes into granulomata. In these infected masses well-known changes, such as those which follow tuberculous infection--atrophy, caseation, calcification, etc.--may be occurring, when suddenly there comes infection of a _pyogenic_ type from another source, and suppuration of the granuloma is the result. It is possible even to have a _tertiary infection_, of which the following may be a hypothetical instance: Primary infection with scarlatina or measles, by which vital susceptibility is in some instances lowered; as the result of this, secondary tuberculous infection in an individual previously resistant; and, third, a suppurative infection, as above described.

In contradistinction to these distinct events, separated by an appreciable, sometimes a considerable, length of time, we recognize a _mixed infection_, where two or more organisms are implanted at or about the same time. An illustration of this is seen in most cases of gonorrhea in which there is a synchronous attack made by the gonococcus, which is a specific microörganism, accompanied by staphylococci or streptococci, whose effect will complicate the case and make it assume a less particulate type of infection. Mixed infections may often occur in other ways, as syphilis and chancroid, chancroid and gonorrhea, etc. Most cases of mixed infection belong rather to surgery than to general medicine, and constitute an apparent violation of the rule to which physicians often point--that two distinct infectious diseases are seldom communicated or acquired at the same time. Nevertheless, the facts remain as above.

=Terminal Infections.=--Terminal infections constitute an apparent paradox, perhaps oftener in medical than in surgical cases. Few people, as Osler has shown, die of the diseases from which they suffer. The final exitus is due to a more or less rapid infection which terminates life. These terminal infections are mainly due to a few well-known microbes, such as the streptococcus, staphylococcus aureus, pneumococcus, bacillus proteus, gonococcus, bacillus pyocyaneus, and the gas bacillus. In surgery such infections are, perhaps, most often seen in malignant lymphoma, diabetes, tuberculosis, syphilis, cancer, and in the so-called surgical kidney.

BACTERIA OF PUS FORMATION.

Bacteria which act as agents in the formation of pus are collectively known as pyogenic organisms. These are divided into two groups:

A. _The Obligate_; and

B. _The Facultative._

_Obligate_ pyogenic organisms are those whose activity is manifested in the direction of pus formation, which seem to produce it if they produce any unpleasant action whatever. On the other hand, the _facultative_ organisms are those which are known occasionally to be

## active in this direction, and yet which are not always nor necessarily

so. The members of group A are fairly well known and catalogued, and are not numerous. On the other hand, there is reason to believe that many organisms may have the occasional effect of producing pus, as it were, by accident or at least in a way not absolutely natural or peculiar to themselves, but still are frequently found when there is no pus present. A suitable list of the facultative organisms, therefore, can hardly be made, and will not be here attempted, the effort being only to mention the more common organisms which play this facultative role. It may be mentioned also that even the adjectives “obligate” and “facultative” are to be accepted with some mental reservation, since staphylococci, for instance, may be met with even in the absence of pus, although nearly all that we know about these organisms implies that pus would be the result of their presence. Furthermore, there are certain other organisms, not, strictly speaking, bacteria, which also have the power of producing either pus or pyoid material. These also will be mentioned in their place. Some of them belong not only to the vegetable, but also to the animal kingdom.

=Obligate Pyogenic Organisms.=

A. =The Staphylococcus Pyogenes Aureus, Albus, Citreus, the Staphylococcus Epidermidis, etc.=--One of the characteristics of the staphylococci as a group is the powerful peptonizing action which they exert. Moreover, the chemical products of their life changes seem to be more potent in a local than a general way, leading to greater destruction of tissue in their immediate vicinity, with greater inhibition of the chemotactic powers of the leukocytes; that is, with more interference with phagocytosis, by which their progress would be interfered with. Their presence is recognized by a peculiar odor, as of sour paste, which should lead to a prompt change of dressings and disinfection of the wound (by irrigation, spraying with hydrogen dioxide, etc.).

B. =Streptococcus Pyogenes and Streptococcus Erysipelatis.=--These two organisms do not differ in morphology nor characteristics, and, while for some time considered as distinct from each other, are now by most observers regarded as identical. The streptococci grow in chains of variable length, and individual cocci vary in size. They grow with and without oxygen, in all media, at ordinary temperatures, do not liquefy gelatin, stain readily, sometimes but not invariably coagulate milk, and vary in longevity. They differ extraordinarily in virulence according to their sources.

[Illustration: FIG. 4

Staphylococci in pus. × 1000. (Fränkel and Pfeiffer.)]

[Illustration: FIG. 5

Streptococci in pus. × 1000. (Fränkel and Pfeiffer.)]

There are many streptococci not included under the above head which are indistinguishable morphologically and in other respects, and yet which are partly or entirely free from pathogenic activity in man. A biological study reveals remarkable and unexplainable transformation between the different members of this species, a part of which may be referable to conditions pertaining to the organisms infected, but part of which apparently pertains to the bacteria. It is held by some that scarlatina is an invasion by certain organisms of this class; this, however, is not yet definitely established. When found in the stools of children with summer diarrheas they are regarded as indicating ulceration of the intestinal mucosa.

In contradistinction to the staphylococci, the streptococci manifest a predilection for lymph vessels and lymph spaces, along which they extend with great rapidity. They have less peptonizing power than the staphylococci (except in the absence of oxygen); hence streptococcus infection assumes usually the type of widespread infiltration rather than of circumscribed and distinct edema. One sees remarkable instances of this in cases of phlegmonous erysipelas. It is suggested also that the peculiar manner of growth of the streptococci, in long chains which may coil up and entangle blood corpuscles, has much to do with the formation of fat emboli and with pyemic disturbances.

Both these bacterial forms have the power of producing lactic fermentation in milk; and lactic-acid formation sometimes takes place with suppuration in the human tissues, causing acidity of discharge, sour odor, and watery pus. It appears also that these two pyogenic forms have less power of ptomain or toxin formation than many others, and, consequently, that the pyrexia attending suppuration or purulent infiltration is not always to be ascribed to this cause alone, for fever may in some measure be due to tissue metabolism attending their growth, the metabolic products being pyretic. This is in a measure substantiated by the fever attending trichinosis, where the question of ptomain poisoning has not yet been raised.

C. =Micrococcus Lanceolatus.=--Micrococcus lanceolatus is also known as the _diplococcus pneumoniæ_ or the pneumococcus of Fränkel and Weichselbaum, and as the _micrococcus of sputum septicemia_ of Pasteur and of Sternberg. It is of interest to surgeons because it causes many localized inflammations and is a frequent factor in causing septicemia; it is often present in the mouths of healthy individuals. It may produce the various forms of exudates as the result of congestion set up by its presence; also otitis media, meningitis, osteomyelitis, and suppurative disturbance in the periosteum, the salivary glands, the thyroid, the kidney, the endocardium, etc.

[Illustration: FIG. 6

Diplococcus pneumoniæ of Fränkel. (Karg and Schmorl.)]

D. =The Micrococcus Tetragenus.=--Suppurations produced by these organisms are prolonged, mild in character, not painful, but accompanied by much brawny induration of tissues.

E. =The Micrococcus Gonorrhœæ.=--The micrococcus gonorrhœæ, or _gonococcus_, is found constantly in the pus of true gonorrhea, in many cases the pus being a pure culture of this organism. These cocci are generally seen in pairs (biscuit-shaped), while their inclusion within the leukocytes or their attachment in or to epithelial cells is characteristic. Unlike other pyogenic cocci, they do not stain by Gram’s method, being decolorized by iodine, by which fact they may be distinguished. They are cultivated with difficulty, and are known rather by their clinical effects than by their laboratory characteristics; are human parasites, other animals, so far as known, being practically immune. The gonococcus may also produce abscesses, and may be carried to distant parts of the body, where its effects are commonly noted as pyarthrosis, although endocarditis, pericarditis, pleurisy, etc., are known to be due to it, and fatal pyemia has been produced in consequence. In some way it is probably the explanation of the post _gonorrheal arthritis_, wrongly spoken of as gonorrheal rheumatism.

F. =The Bacillus Coli Communis or Colon Bacillus.=--This is an inhabitant of the intestinal canal; varies extremely in virulence and somewhat in morphological appearances; coagulates milk; is often associated with other organisms; migrates easily both along the alimentary canal and from it into the surrounding tissues or channels. It is a disturbing element in the production of kidney and hepatic disease, also in the production of appendicitis and peritonitis. Ordinarily its pyogenic properties are not virulent; occasionally, however, it becomes extremely virulent.

G. =The Bacillus Pyocyaneus.=--The bacillus pyocyaneus, a widely distributed organism, often observed in the skin and outside of the body; a motile, liquefying bacillus, growing at ordinary temperatures, seldom seen alone, but occasionally producing pus without association with other organisms; it stains the discharges and dressings a bluish-green and imparts sometimes an offensive odor. Suppuration caused by this bacillus is usually prolonged, but characterized by little constitutional disturbance.

=Facultative Pyogenic Organisms=--_i. e._, those which have the power of provoking suppuration, but which have other and more distinct pathogenic activities as well.

A. =Bacillus Typhi Abdominalis.=--This is found in many pus foci, developing during or after typhoid fever. It is occasionally met with alone, though most of these abscesses are really mixed infections. It is generally found in the bone or beneath the periosteum. Such abscesses are frequently seen in the ribs, and may not be noticed until months after convalescence from the fever. The pus contained within them is not always typical in appearance, but may be unduly thin or unduly thick.

B. =Bacillus Proteus.=--Under this name are included three distinct forms, which were originally described by Hauser as distinct species, but which are now regarded as pleomorphic forms of the same organism. It is a motile bacillus, met with in decomposing animal and vegetable material, and occasionally found in the alimentary canal. It has been known to produce pus, especially in the peritoneal cavity and about the appendix. It may even cause general infection and peritonitis.

C. =Bacillus Diphtheriæ.=--A non-motile bacillus, varying considerably in size and shape, changing the reaction in sweet bouillon from acid to alkaline; produces a dangerous infective inflammation of exposed surfaces, with tenacious exudate amounting to a distinct membrane. As a part of its life history it also produces a toxalbumin, which is one of the most powerful cell poisons known, the disintegration of the cell constituents due to its action being rapid and pronounced. This accounts for the heart failures which are often reported in connection with the disease.

D. =Bacillus Tetani.=--More will be said about this organism when considering tetanus, and to that subject the reader is referred. The tetanus bacillus is occasionally found in pus which comes from the area through which the original infection was produced. But these bacilli do not travel to any distance in the human body, and are seldom found away from the area involved. Under most circumstances the pus is the product of a mixed infection.

E. =Bacillus Œdematis Maligni.=--This organism will be more fully considered under a different heading. (See Malignant Edema.) It is a long, anaërobic bacillus, widely distributed in the soil and the feces of animals. It is believed that this, like the tetanus bacillus, may occasionally lead to formation of pus.

F. =Bacillus Tuberculosis.=--This organism likewise will receive fuller description in an ensuing chapter. (See Tuberculosis.) The pus of old cold abscesses in which the more obligate pyogenic organisms have long since died usually contains this organism in mildly virulent form. On the other hand, fresh suppurations occurring in connection with tuberculous disease are mixed infections. There is reason to believe, however, that this organism is capable of producing pus even when none of these are present; for example, in that form of acute miliary tuberculosis which is occasionally met with as bone abscess it may be found.

G. =Bacillus Anthracis.=--This is one of the most malignant and resistant organisms known, being in the highest degree poisonous for the smaller animals, man being less susceptible. One of its characteristic lesions in the human body is a form of pustule commonly known as _malignant pustule_, the pus in which is usually a pure culture of this organism. (See Anthrax.)

H. =Bacillus Mallei.=--This is the organism which produces glanders in the lower animals and in man. That form of the disease known as farcy, in which the infected nodules rapidly break down, is likely to contain pus which will be more or less a pure culture of this organism.

I. =Bacillus Lepræ.=--This is the microörganism which produces leprosy, closely resembling the tubercle bacillus. It is constantly and exclusively present in the lesions of leprosy, which are often of the suppurative type, the bacilli being enclosed within pus cells; it is also found in the fluid surrounding them. Although suppuration in these cases may be in a large measure due to secondary infection, it is positive that the leprous bacilli deserve to be grouped in this place.

J. =The Bacillus Pneumoniæ of Friedlander.=--The bacillus pneumoniæ of Friedländer was at one time regarded as the cause of croupous pneumonia, which is now known to be due to the micrococcus lanceolatus. The Friedländer bacillus, however, is capable of producing bronchopneumonia, and is occasionally met with in empyema, suppurative meningitis, and inflammations about the nasopharyngeal cavity, of which it is known to be an occasional inhabitant.

K. =The Bacillus of Rhinoscleroma.=--A distinctive organism has been described for this disease and given this name. It has such wide morphological differences, however, that it is possible that it is only the bacillus of Friedländer above mentioned. At all events, an organism of this general character is constantly found in this disease in the thickened tissues from the nose (Fig. 8).

L. =The Bacillus of Bubonic Plague.=--This was recently discovered by Kitasato, and, in view of the recent ravages of the disease in the Orient, has assumed considerable importance. It grows upon most media, and is found in the blood, in buboes, and in all internal organs of patients suffering from this disease. The smaller animals are susceptible upon inoculation. Animals fed with inoculated foods die also, showing the possibility of infection through the intestine. When exposed to direct sunlight for a few hours the bacillus dies. The general symptoms of the disease are those of hemorrhagic septicemia and its consequences.

M. =The Bacillus of Rauschbrand.=--This is seldom, if ever, seen in this country. It is known in England as “the black-leg” or “quarter-evil.” It is an anaërobic organism, frequently met with in cattle, which causes a peculiar emphysema of subcutaneous tissue, spreads deeply, and is followed by a copious exudate of dark serum with gas formation. The smaller animals are not ordinarily inoculable; but if to the culture material there is added 20 per cent. of lactic acid, their insusceptibility is overcome and they succumb to the disease. So, also, as in the case of the tetanus bacillus, by addition of the bacillus prodigiosus or of proteus vulgaris the disease may be produced in otherwise insusceptible animals.

N. =The Bacillus Aerogenes Capsulatus.=--The bacillus aërogenes capsulatus seems capable sometimes of causing pyogenic and even fatal infection. Its presence is associated with gas formation. It grows as an anaërobe.

O. =The Bacillus of Chancroid.=--The bacillus of chancroid identified by Ducrey, and briefly described in the chapter on that subject.

[Illustration: FIG. 7

Rhinoscleroma: infiltration of tissues about the nose. (Case reported by Dr. Wende, Buffalo.)]

[Illustration: FIG. 8

Bacilli of rhinoscleroma. × 1000. (Fränkel and Pfeiffer.)]

YEASTS.

Busse was the first to call attention of clinicians and pathologists to the role played by yeasts in certain infections. Since the original observations of Busse in a case in which the organism produced a general infection, the lesions of which were a combination of tumor and abscess formation, various observers have noted the presence of pathogenic yeasts, usually in skin lesions. Gilchrist and Stokes were the first in this country to determine the nature of these organisms, and their observations have been followed by the detection of a large number of similar cases. In the skin lesions the organisms are found in minute abscesses; in the subcutaneous tissue and in the infections similar to those of Busse large abscesses surrounded by extensive masses of granulation tissue characterize the infection. The organisms can be detected in the pus by means of an examination of the fresh unstained fluid (Fig. 9).

FUNGI.

Besides the micro-organisms everywhere grouped as bacteria, there are other minute organisms which have also the power of engendering pus. One of these is the ray fungus, known as the _actinomycis_, which causes the disease known as lumpy jaw or actinomycosis. Suppuration is always a concomitant of the advanced lesions of this disease, and, while it may be in many instances a mixed infection, it is not necessarily so. Moreover, the pus produced under these circumstances contains minute calcareous particles which are pathognomonic, by which a diagnosis can sometimes be made off-hand.

Besides these fungi, others, belonging rather to the class of vegetable molds, which are yet pathogenic for human beings, may be occasionally met with under these circumstances--_e. g._, _the fungus of Madura foot_, the _leptothrix_, and other molds from the mouth, while the different varieties of _aspergillus_ may be found in pus about the ear or even in that from the brain.

PROTOZOA.

The protozoa have the power of producing, if not absolute ideal pus, something so nearly resembling it that we may include them among the facultative pyogenic organisms. The best known of these protozoa are the _amebæ_, which are met with in the intestinal canal in some countries, occasionally in the United States, especially as the exciting causes of a peculiar type of dysentery often accompanied by abscess of the liver. In these abscesses the amebæ are found, and no other organisms. Another group of the protozoa, known to biologists as the _coccidia_, are also capable of causing pus formation, more

## particularly in some of the lower animals. Numerous other parasites,

belonging higher in the animal kingdom, are undoubted exciters of pus formation, though it is not necessary to lengthen the list beyond those already mentioned.

[Illustration: FIG. 9

Blastomycetic pus (fresh). × 1000. (Gaylord.)]

Protozoa have recently been established as the active agents in the production of smallpox and probably also of scarlatina. They have been seen so generally in and around cancer cells as to make it extremely probable that cancer is a protozoan infection. In syphilis also they are found as the _spirochetæ_, now regarded as its cause.

Protozoa are as ubiquitous as bacteria, but their recognition is as yet more difficult, as but little is known of them. The numerous stages through which they pass in completing their life cycles only complicate the subject, while the difficulties encountered in cultivating them are still to be overcome. As we become more familiar with them we shall more frequently find them to be pathogenic organisms.

CLINICAL CHARACTERISTICS OF PUS FROM DIFFERENT AGENCIES.

_Staphylococcus._--Dirty white, moderately thick, with sour-paste odor.

_Streptococcus._--Thin, white, often with shreds of tissue.

_Colon Bacillus._--Thick, brownish, with fetid odor, or thin, dirty white, with thicker masses.

_Micrococcus Lanceolatus._--Thin, watery, greenish, often copious.

_Bacillus Pyocyaneus._--Distinctly green or blue in tint.

_Bacillus Tuberculosis._--Thick, curdy, white paste, or thin, greenish, with small, cheesy lumps or even with bone spicules.

_Actinomycis._--Thick, brownish white, with small, firm, gritty or chalky nodules of yellow color.

_Ameba Coli._--Thick, brownish red.

BACTERIAL DETERMINATION AS AN INDICATION IN TREATMENT.

There is a practical side of great importance pertaining to the recognition of the nature of the infectious organism in many cases of suppuration and abscess. For instance, pus which is due to streptococcus invasion indicates a collection which should be freely evacuated and carefully drained. This is also true in essential respects of staphylococcus pus, particularly that due to the streptococcus aureus. Putrid pus from any source requires disinfection and free drainage, the former preferably perhaps by hydrogen dioxide. Pus which is due to the colon bacillus is not often extremely virulent, which accounts for so many cases of appendicitis recovering with or without operation. A collection of this pus needs little more than mere drainage and opportunity for escape. Pus from a recognizable tuberculous source may still contain living tubercle bacilli. This means either that the cavity whence it came should be completely destroyed and eradicated, or else that the margins of the incision or opening through which it has escaped should be so cauterized that infection of a fresh surface is impossible. The same is true of abscesses due to glanders bacilli and to certain cases of suppurating bubo following chancroid, where the whole course of events shows the virulent character of the organisms at fault.

SUPPURATION.

Although it may be possible to produce in certain laboratory experiments metamorphosed material which very closely simulates pus, or, in fact, by injection of chemical irritants, to sometimes imitate the suppurative processes, nevertheless, the student should be brought face to face with the statement, to which for surgical purposes there is no practical exception, that suppuration, _i. e._, _formation of pus, is due to the presence in the tissues of the specific irritants already catalogued and described, and of the peculiar peptonizing or other biochemical changes which bacteria exert upon living animal cells_.

=Coagulation Necrosis.=--Coagulation necrosis is the term applied to the characteristic changes occurring in the tissue cells when thus attacked, which may be summarized as a fading away of cell outlines, diminution in reaction to reagents, and a merging of cells and intercellular substance. Coagulation necrosis is not the only result of bacterial activity, but may be produced by other causes. Nevertheless, pyogenic bacteria do not exert their deleterious action upon the tissues without occasioning changes included under this term. In an area thus infected, as already described, leukocytes, _i. e._, phagocytes, are present in increased number for purposes already mentioned. As we approach the centre of activity phagocytes are more numerous than cells, and intercellular barriers completely break down. When bacteria are found in greatest number, there also occurs the greatest phagocytic activity, and there also will be found the evidence of suppuration, _i. e._, _pus_. As already indicated, the _polynuclear leukocytes_ are most active in the process of defence. Where coagulation necrosis is most marked there has been the greatest

## activity of conflict with the greatest death of cells. Around these

areas bacteria and cells are found in indiscriminate arrangement. Tissue vitality is impaired by intoxication of the cells by the excretory products of the bacteria, _i. e._, the so-called ptomains, toxins, etc., and their power of resistance is thus weakened. From the mechanical results of pressure tension around the centre of activity is increased, by which tension vitality is still more impaired and more rapid tissue death occurs. Thus there occurs migration or burrowing of pus; or, to state it more clearly, the tissues break down in front of the advancing destruction, and in the direction of least resistance. This is known as the _pointing of pus_, which brings it many times to the surface, and often in other and less desirable directions.

=Abscess.=--An abscess is a _circumscribed collection of pus_. The term is used in contradistinction to _purulent infiltration_, in which the collection is not circumscribed, but is exceedingly diffuse and extends itself in various directions, the amount at any spot being almost inappreciable. Purulent infiltration is regarded as the more serious of the two conditions, as it is more difficult for pus to escape under these circumstances than when it can be evacuated through a single opening. The term _phlegmon_ is one now generally used to indicate a suppurative process, usually of the general character of purulent infiltration rather than of abrupt abscess, but generally employed to include both conditions. The adjective _phlegmonous_ is coupled with the names of other surgical infectious diseases to indicate that it is complicated by suppuration, _e. g._, phlegmonous erysipelas. _Pus_ is a product of bacterial activity usually formed rapidly rather than otherwise, and abscess formation or phlegmonous activity of any kind is a question of but a few days. _Empyema_ means a collection of pus in a preëxisting cavity.

The significance of this condition is well described in the story of inflammation and suppuration, to paraphrase Sutton, read zoölogically, as though it were the story of a battle: The leukocytes (phagocytes) are the defending army, the vessels its lines of communication, the leukocytes being, in effect, the standing army maintained by every composite organism. When this body is invaded by bacteria or other irritants, information of the invasion is telegraphed by means of the vasomotor nerves, and leukocytes are pushed to the front, reinforcements being rapidly furnished, so that the standing army of white corpuscles may be increased to thirty or forty times the normal standard. In this conflict cells die, and often are eaten by their companions. Frequently the slaughter is so great that the tissues become burdened by the dead bodies of the soldiers in the form of pus, the activity of the cells being proved by the fact that their protoplasm often contains bacilli in various stages of destruction. These dead cells, like the corpses of soldiers who fall in battle, later become hurtful to the organism which, during their lives, it was their duty to protect, for they are fertile sources of septicemia and pyemia. This illustration may seem romantic, but is warranted by the facts.

Around the margin of the site of an acute abscess a barrier is formed by condensation and cell infiltration of the surrounding tissues. This is not a distinct wall nor membrane, yet, nevertheless, serves as a sanitary cordon to confine the mimic conflict within reasonable bounds. This is the zone of real inflammation; within it there are tissue destruction and coagulation necrosis. By virtue of the peptonizing power of the pyogenic organisms the parts involved in this necrosis gradually liquefy the intercellular substance dissolving first. It is this which in the main forms the fluid portion of the pus. Various tissues show widely differing resistance to this softening process. In true glands the interlobular septa seem to break down first, and in this way suppuration extends around the acini or gland lobules, and thus pus may contain masses of easily recognizable size. These masses are ordinarily known as _sloughs_.

It is by virtue of the so-called lymphoid cells, which are those principally involved in producing the barrier or boundary of the acute abscess as above described, that granulation tissue is formed, which takes up the effort of repair as soon as pus is evacuated. This boundary has no sharp limit, but shades off into healthy surrounding tissues.

Under the term “abscess” is meant that which is described as _acute abscess_. Under certain circumstances, especially when they are produced by the facultative pyogenic organisms rather than the obligate, abscesses form more slowly, and may be spoken of as _subacute_. These are terms used in contradistinction to the so-called _cold abscesses_, which, although clinically bearing a certain resemblance to the acute, are in almost every pathological respect different from it. Cold abscesses will be considered under the head of Tuberculosis. It is possible to have an acute pyogenic infection of a cold abscess; in such case we have acute manifestations. _Gravitation abscesses_ are those where pus forming in one part tends to migrate, usually in the direction in which gravity would take it, extending into portions deeper or lower. Perhaps the best illustration of this is the pointing of a psoas abscess below Poupart’s ligament. _Metastatic abscesses_ are those which are formed as the result of embolic processes, each one being in miniature a repetition of a lesion which has occurred at some other part of the body. The underlying fact concerning metastatic abscesses is that the primary process has occurred in some other portion of the body, whence it has been distributed as above. These will be considered in the chapter treating of Pyemia.

The product of all acute suppurative lesions is _pus_. This is an opaque fluid of creamy consistence and whitish or grayish appearance, varying in density, met with in amounts from a minute drop to half a gallon or more. Under ordinary circumstances it is odorless, and its reaction, either acid or alkaline, is very faint. It is, like the blood, composed of a fluid and a solid portion. The solid portion consists of so-called _pus corpuscles_ and other debris of tissue, which vary with the site of the disease and the parts involved. The source of the pus corpuscles has been cited and the statement made that they are in effect the bodies of phagocytes which have perished in the biochemical fight for existence of the parent organism. Cocci or bacilli are found in pus corpuscles and also in the surrounding fluid.

Pus should be without odor, but under certain circumstances it possesses an odor which will vary in character according to the source of the pus or the nature of its principal bacterial excitant. Pus from the upper end of the alimentary canal frequently has the sour smell of gastric contents; that from the neighborhood of the lower end, the fetid odor which is for the most part due to the action of the colon bacillus. Inasmuch as colon bacilli are found in widely distant parts of the body, they may also give an unpleasant odor to pus even from a brain abscess. When the pus has become contaminated with the ordinary saprophytic organisms, it may smell like any other decomposing material. The older writers called it _ichorous pus_, while _sanious pus_ was supposed to be that more or less mixed with blood, undergoing ammoniacal decomposition or else strongly acid. Pus sometimes has a well-marked _blue_ or _bluish-green tint_. This is due to the presence of the _bacillus pyocyaneus_, already described. An orange tint is sometimes given by the presence of hematoidin crystals, due to the original hemorrhagic character of the infected exudate. The former appearance indicates usually a slow course to the suppurative lesion, while the latter has been regarded by some as affording an unfavorable prognosis. Distinctly red pus, whose tint is due to the presence of a bacillus giving bright-red cultures on blood serum, has been noted in other instances. This can readily be distinguished from blood, because upon dressings it does not change color.

Pus may form superficially, when it is called subcutaneous suppuration, in which case there is a minimum of pain, because tension is not great and the distance to the surface is short. Collections which form beneath the fasciæ, especially the deeper fasciæ of the limbs and trunk, give rise to much more extensive disturbance, both locally and generally, and frequently do not point for many days; or, instead of pointing, burrow deeply and find their outlet at some undesirable point. These are known as _subfascial_ collections. _Subperiosteal_ abscesses give rise to still more pain, because of the unyielding character of their limiting structures, and the symptoms caused by them are acute and distressing.

An illustration of the pain which may follow deep suppuration may also be seen in the ordinary panaritium, or bone felon, where the path of infection is from without, but the destructive lesion is confined within absolutely unyielding tissues, at least at first. Along certain tissues infection spreads with rapidity. This is particularly true of the delicate areolar tissue seen between tendons and tendon sheaths, and the infectious process may follow this tissue wherever it shall lead, even along complex courses.

The question often arises, _Can pus be resorbed?_ There is no question but that small amounts of pus are disposed of by phagocytic activity, and the disappearance of purulent infiltration, under the influence of favoring remedies, or even when let alone, is not infrequently noted. True pus resorption is a question of phagocytic possibilities, and can occur only in very limited degree, as a result upon which it is not safe to count, and which is capable of encouragement only up to a certain point.

One inevitable law seems to govern collections of pus, that when they _advance_ or migrate in any direction it is in that of _least resistance_. This causes them to take peculiar and sometimes disastrous courses, but it is a law which is never violated. It leads to the bursting of abscesses into the brain, into the pleural cavity, into the peritoneal cavity, the bowel, and elsewhere; it leads to a condition where pus may travel along a path even a foot or more in length, rather than come to the surface, a distance of perhaps an inch, and affords one of the best reasons for early operative interference so that the disastrous effects of burrowing may be obviated. When the pus is limited to a drop or fraction thereof the abscess is called a _furuncle_, especially when in the skin. The average “boil” of the layman is a subcutaneous or subfascial abscess. When the infiltration is pronounced, and when there has been more or less extensive destruction of tissue, with perhaps formation of numerous outlets for the escape of pus and detritus, it is known as a _carbuncle_. (See

##