Part 12

If our examination of the mouth discloses anything likely to interfere with mastication the aid of the dentist should at once be sought, but every physician should be so far acquainted with disorders of the teeth as to be able to say, in the majority of cases, at all events, when this is necessary. I am convinced that far more illness than is generally supposed is attributable to dental defects, and this even among the more leisured classes. With regard to pyorrhœa alveolaris, it has to be remembered that it not only does harm by causing loosening, lengthening, and shedding of the teeth, and thus interfering with mastication, but also by contaminating the stomach and the blood and thus upsetting the digestion and causing constitutional diseases, such as anæmia and arthritis; and inasmuch as poisonous discharges from the nose, the naso-pharynx, the pharynx, and the tonsils may act in a similar way, these parts also should be inspected in connection with the examination of the teeth. In the dust-laden atmosphere of towns they are very liable to disease, and even when healthy are necessarily dirtied; some go so far as to advise all town dwellers daily to wash out the nasal passages and to gargle the throat; but, whatever may be thought of this, it is certain that under existing dietetic conditions special means are needed in order to keep the mouth and teeth clean. When man fed on raw food this was not necessary, the food itself and the copious flow of saliva, induced by prolonged mastication, effectually cleansing these parts; but, under present conditions, food tends to remain within the mouth, especially between the teeth and in their crevices, and therefore special means are needed to remove it. This is done by “cleaning the teeth” and by rinsing the mouth.

_The tooth-brush._--Probably the ideal method of cleaning the teeth is that adopted by many primitive and not a few semi-civilised peoples--viz., rubbing them with a twig of wood which has been teased out at one end so as to form a sort of brush by means of which the teeth can be burnished and food dislodged from them. The modern tooth-brush requires to be used with great caution, as it is capable of doing much harm, not only by removing the mucoid film, which, according to Dr. Wallace, protects the teeth from corroding agencies,[28] but probably also by injuring the edge of the gum and the neck of the teeth, and thus setting up the condition known as “erosion.” Certain it is that some of the best sets of teeth I have encountered have been wholly unacquainted with the tooth-brush. In any case the brush should be employed with great care; it should be soft, and should always be drawn away from the gums both on the inner and outer aspect of the teeth towards the biting surface, as well as across the latter, never transversely across the outer surfaces, as so frequently is done. The object of these procedures is to dislodge any particles of food that may have collected between the teeth or in their crevices. For this purpose the toothpick may also be employed judiciously. In order to render the enamel of the teeth white it is better to rub each tooth carefully with some soft material, such as chamois leather, rather than to scrub them with a brush. Tooth-powders should not be used as a matter of routine, but only occasionally and for appearance rather than for cleanliness, and should consist of some simple non-irritant material. Antiseptic powders and washes are to be scrupulously avoided, for it is neither desirable nor possible to render the buccal cavity aseptic; myriads of bacteria flourish within it, many of which play a useful part as scavengers. The time of all others for cleaning the teeth is just before going to bed, so that the food shall not be allowed to decompose in the mouth during the night. There will then be no need to use the tooth-brush in the morning.

_Rinsing the mouth._--The mouth should be rinsed out as a matter of routine after each meal and on rising, and care should be taken to do this before the early cup of tea, so as not to contaminate the stomach with the buccal secretions which have accumulated during the night. Inasmuch as raw vegetable food has a cleansing effect on the teeth, it is often a wise plan, especially in the case of children, to finish a meal with some kind of fruit, such as an apple or an orange. It hardly seems necessary to insist upon the necessity for keeping all artificial dentures thoroughly clean.

PROFESSOR PAWLOW’S DEMONSTRATIONS OF PSYCHIC INFLUENCE IN DIGESTION

[In presenting a theory of human alimentation involving mental or nervous as well as mechanical and chemical factors which influence it for good, it is not often that an author is able to enlist the assistance of a complete battery of scientific confirmation to fortify his own crude observations taken direct from personal experience in the study of natural requirements.

Professor Pawlow, with his marvellously skilful investigation of the workings of the digestive secretions, and Dr. Cannon of the Harvard Medical School, by aid of persistent and patient X-ray studies, explain how it is that earned appetite and thorough mouth-treatment of food are preliminary necessities of easy digestion, and that disturbance or shock of any sort during the process stop digestive proceedings and endanger health. They show also that when the mouth is used to do _all that it can do_ in the work of digestion all the rest is easily accomplished by the NATURAL AUTOMATIC PROCESSES within the body.

They both show that we have, each of us, a certain responsibility in the matter of right digestion and healthy nutrition, and that all this personal responsibility is located in the head, in the mind, and in the mouth, and that while the alimentation is proceeding it is a sacred duty to do our part _right_, according to the intelligence that these most valuable demonstrations teach.

Professor Pawlow has allowed publication of his lectures in Russian and German, and recently Professor W. H. Thompson of the Physiological Department of Trinity College, Dublin, has made an English translation which is issued by Charles Griffin & Company of London and J. B. Lippincott of Philadelphia.

The author has to express special gratitude to Professor Pawlow, Professor Thompson, Messrs Griffin and Lippincott for permission to reprint herein some entire lectures and extracts that bear especially on the practical understanding of our subject.

Professor Pawlow is one of the Board of Scientific Assessors mentioned in the REPORT of a PLAN for an INTERNATIONAL INQUIRY into the subject of HUMAN NUTRITION.

In one of the lectures, not here reprinted, Professor Pawlow gives merited recognition of the early statements of the French physiologist Blondlot relative to psychic influence on the digestive secretions made some half century ago, but discredited by physiologists since that time, owing to insufficiency of evidence brought forward in support of the statements.

Professor Pawlow’s acknowledgment is so gracefully rendered that it is here given as a model of scientific courtesy.

“I have depicted the work of the gastric glands as we have seen it in our experiments, and as it has developed under our hands. Is the picture a new one? In its details, yes; but not in its fundamental features. However singular it may appear, the sketch of this picture was more than fifty years ago outlined by physiology. May this constitute another reason for our science relinquishing its characteristic shyness of new things and for its conversion to our interpretation of the phenomena under consideration!

“The talented author of the _Traité Analytique de la Digestion_--Blondlot--spoke in plain words of the importance of taking food, and of the specific excitability of the gastric mucous membrane. The facts adduced in the working up of his theory were naturally insufficient, but we must not forget that the first experiments on dogs with artificial gastric fistulæ had only just been performed. It is truly incomprehensible that the researches of Blondlot and his views upon the secretion of gastric juice have experienced during the past fifty years no completion, no additions, but, on the contrary, have passed out of sight, thanks to the faulty experiments and erroneous representations of later authors. Only in the works of a few writers--and those mostly French--has Blondlot’s theory survived. Of other investigators we must give mention to Heidenhain, who has enriched the physiology of absorption in general, but more especially, in connection with the secretory work of the stomach, has discovered many important facts and has given birth to many fruitful ideas. From him proceed the subdivision of the secretory process according to periods and exciting agencies, as well as the suggestion that it would be important to investigate the individual food-stuffs in relation to the work of the stomach. Heidenhain’s results are contained in his well-known article on the secretion of the cardiac glands of the stomach, published in the year 1879 in PFLÜGER’S ARCHIVES. The work of Blondlot and the additions of Heidenhain comprise almost everything of importance which was accomplished by physiology in fifty years concerning the conditions and mechanism of the secretory work of the stomach during digestion. Full of moment, however, for our subject was the obvious error that mechanical stimulation constituted an effective excitant of the gastric glands, and this error was in its turn a result of faulty methods.”—HORACE FLETCHER.]

LECTURE IV

GENERAL SCHEME OF AN INNERVATION MECHANISM--THE WORK OF THE NERVOUS APPARATUS OF THE SALIVARY GLANDS--APPETITE, THE FIRST AND MOST POTENT EXCITER OF THE GASTRIC SECRETION

Constituent parts of a complete innervation mechanism--The special duty of the peripheral terminations of afferent nerves--The specific qualities of nerve cells--Analogy between the innervation mechanism of the salivary glands and that of the deeper-lying glands of digestion--The exciting agencies of the nervous mechanism of the salivary glands; their particular properties--Differences between the exciting agencies of the different salivary glands--Discussion of the sham feeding experiment--Mechanical and chemical stimulation of the cavity of the mouth has no effect on the gastric glands--The experiment of Bidder and Schmidt relative to psychic excitation of the gastric secretion--Conditions for success in this experiment--The passionate longing for food--the appetite--alone brings on the secretory effect in the sham feeding experiment.

GENTLEMEN,--As you have learned in the last lecture, and also in part have seen by direct experiment, the nervous system can influence the work of our glands in the most diverse ways. The vagus nerve, already burdened with many duties, has, in addition, proved itself to be an undoubted exciter of the gastric glands and of the pancreas. But we must also assign to the sympathetic nerve a similar _rôle_. This is a matter which cannot be doubted, so far as the pancreas is concerned, and is highly probable as regards the stomach. We also saw good reason for believing that these two nerves contained two different classes of fibres, secretory and trophic, a condition which had already been proved to exist by Heidenhain for the nerves of the salivary glands. As a hypothesis we might even have proceeded a step farther and have divided Heidenhain’s trophic nerves into separate classes of secretory fibres. Lastly, we advanced important experimental evidence to show the existence of special inhibitory fibres to the glands, and these fibres also run in the vagus, the list of whose functions seems almost interminable.

We obtained these results by division and artificial excitation of the nerves which run to the glands. But when, how, and by what means these nerves are thrown into activity during the normal course of physiological events remains a question.

In order to avoid repetition, and at the same time impart the utmost clearness to our representation, it may be useful to bring before your minds at once the plan of innervation of a given organ, all the more since this scheme is seldom completely followed out or adequately described in physiological text-books. Consequently, it is not borne in mind with sufficient precision by the majority of medical men.

A complete innervation mechanism consists of the peripheral endings of the centripetal (afferent) nerves, the centripetal nerves themselves, the nerve cells (a group of nerve cells connected with each other is termed a “nerve centre”), the centrifugal (efferent) nerves, and, lastly, their peripheral terminations. Physiology now accepts it as a settled fact, that nerve fibres serve only as _conductors_ of nervous impulses, which come in from contiguous links of the nervous chain. Only the peripheral endings of nerves and the nerve cells themselves have the power of transforming the external stimulus[29] into a nervous impulse. In other words, in the intact organism these alone constitute the normal receiving apparatus of the nervous system. Whether the peripheral ends of centrifugal (efferent) nerves are likewise able to function as normal sites for the application of external stimuli has still to be answered. Consequently, when any external agency excites the peripheral terminations--the receiving stations--of centripetal nerves in this or that organ, the effect of the stimulus will be conveyed through the centripetal nerves, as through a receiving wire, to the central station--the nerve cells. Here it becomes changed into a definite impulse and now comes back along the centrifugal nerves--the outgoing wires.

The utmost importance is to be attached to the fact that only the peripheral endings of centripetal (afferent) nerves, in contrast to nerve fibres themselves, respond to _specific_ stimuli; that is to say, are able to transform definite kinds of external stimuli into nervous impulses. The function of the end organs with which they are connected is therefore of a purposive nature; in other words, these organs are only called into play by certain definite conditions, and impart the idea of being aware of their purpose, of being conscious of their duty. We have long known that the peripheral endings of sensory nerves are possessed of a high degree of speciality, and cannot therefore have any doubt regarding the specific nature of the end organs of other centripetal nerves. This is a sore point in present-day physiology. But, notwithstanding our knowledge of the separate parts of the animal body, we shall only be able to form a true conception of the motive agencies of the whole complicated machine, when we have established the specific excitability of the end apparatus of every centripetal nerve, and have discovered all the mechanical, chemical, and other factors which throw this or that end apparatus into an active condition. I always look upon it as a period of scientific inadequacy so long as the effects of the most diverse external agencies upon any normal physiological process are admitted to be indistinguishable. As the work of the digestive canal is now represented in the majority of text-books, and consequently presented to the mind of the physician, it bears the impress of this period. To impart to the physician a more correct conception of this matter was my chief object in giving these lectures. I hope, indeed, to furnish you with evidence sufficiently convincing, that the alimentary canal is endowed not with mere general excitability; that is to say, does not respond to every conceivable form of agency, but only to special conditions which are different for the different portions of its length. Just as men and animals in the world are only able to maintain their existence and constantly adapt themselves to changing circumstances by aid of the peripheral endings of their sensory nerves, so every organ, indeed every cell of every organ, can only maintain its place in the animal microcosm, and adapt itself to the activity of innumerable associates, as well as to the general life of the whole, by virtue of the fact that the peripheral end apparatus of its centripetal nerves possesses a specific excitability.

The same applies to the nerve cells: obviously they are endowed with specific sensibility. Irrespective of the excitations which are communicated to them from centripetal nerves, they respond, as originators of nervous impulses, only or at least mainly to definite forms of mechanical, chemical, or other stimuli arising in the organism. This follows not alone from a number of physiological facts but also from various pharmacological data. Thus we learn that various drugs excite or annul the activity of definite portions of the nervous system, at least in the earlier phases of their effects. This specific excitability of nerve cells, just as much as the same property of peripheral end organs, lies at the bottom of the purposive action of these organs.

Hence, our next duty is to endeavour to discover the normal exciting conditions of the centripetal nerves belonging to the glands which we had under consideration in our last lecture, or, more correctly, to find out the conditions which excite the centres, as well as the peripheral endings of the different nerves, which form parts of the nervous apparatus of these glands. We have, therefore, for each phase of the work of secretion, to find out that portion of the nervous mechanism which is for the time being under excitation, and to discover the primary agency by which this condition is elicited. This would include an exact analysis of the stimulating influence which mastication and food exert upon the nervous mechanism of these glands. We shall also be able more fully to comprehend the inner mechanism underlying the facts which formed the subject of the second lecture. This, of course, is an ideal programme which we can only follow out as far as the present state of physiology permits. It may now be instructive, and, for our further conclusions, advantageous, to glance shortly at the nervous control of the salivary glands.

The salivary glands, whose innervation has long ago been investigated, have generally been accepted as types of the deeper-lying digestive glands, and when it became necessary to form a conception of the mode of activity of the latter, medical science resorted to a bold analogy and thought of the nervous apparatus of the salivary glands. But the attempts of investigators to apply rigidly to others the scheme of innervation which holds good for the salivary glands, have done considerable harm to the usefulness of the analogy and have prevented our arriving at a correct idea of the plan of innervation of the abdominal glands. We have already had an example of this nature before us. In the salivary glands we have no clearly marked indications of nervous inhibition, and this circumstance has decidedly retarded the due development of our knowledge of the nervous control of the abdominal glands. Authors naturally expected to see a simple and prompt stimulation-effect from the same conditions of experiment which sufficed for the salivary glands, and the failure of this gave them, as they thought, the right to deny the existence of any extrinsic nervous influence upon the abdominal glands. The error is now obvious; the abdominal glands behave in some ways different from the salivary glands, and for their successful investigation, other conditions of experiment are necessary than those which held good for the former. In the working of the abdominal glands nervous inhibitory processes play a large part, but they are almost wholly absent in the case of the salivary glands. This is an additional warning that one must never push the conclusions drawn from analogy too far, but must constantly bear in mind that the life-functions of all organs are extremely complicated, and that the work of even the most apparently similar organs should be submitted to separate and careful observation. To me it appears that the unjustified analogy drawn between the abdominal and salivary glands has to be credited with another important misapprehension. And precisely for this reason I think it desirable to bring under consideration, if only in brief fashion, the conditions of work of the salivary glands, especially since Dr. Glinski has instituted in the laboratory some easily performed experiments which bear upon the matter.

The experiences of daily life teach us from the outset, that the

## activity of the salivary glands begins even before the introduction

of food into the mouth. With an empty stomach, the sight of food or even the thought of it is sufficient to set the salivary glands at once into activity; indeed, the well-known expression, “to make one’s mouth water,” is based upon this fact. Hence a psychic event, the eager longing for food, must be accepted as an undoubted excitant of the nervous centre for the salivary glands. On the other hand, the same every-day experience, as well as numerous experiments upon animals, teach us that a number of substances, when brought into contact with the mucous membrane of the mouth, are likewise able to call forth a secretion of saliva. One even acquires the impression that everything brought into the mouth may reflexly influence these glands, the only difference being a gradual shading off in the effect, dependent upon the strength of the stimulation which the substance introduced is able to exert, and it appears to me that it is precisely this impression which has driven the idea into the background, that the peripheral end apparatus of the centripetal nerves of the digestive canal are specifically excitable. The facts were here correctly observed, but their indications erroneously interpreted.

The great multiplicity of excitants of salivary secretion, has without doubt, some connection with the complicated physiological functions of the saliva. This is the first fluid encountered by everything which enters the alimentary canal. It must, therefore, in a sense play the part of host to every substance taken in--moisten the dry, dissolve the soluble, envelop the hard and bulky with mucus in order to facilitate its passage down the narrow œsophagus; and submit certain forms of food material, such as starch, to a process of chemical elaboration. Nor is its duty by any means ended here. The saliva is secreted in the first compartment of the alimentary canal, which is at the same time the sorting-room of the organism. Much of what enters the mouth may prove in the testing process to be useless, or even noxious, and must either have its deleterious properties neutralised or be completely rejected. The saliva is secreted in the first instance to obviate injurious effects in some way; thus, for example, a strong acid is to a certain degree neutralised, while other corroding substances may be simply diluted, and by mere reduction of concentration have their harmfulness diminished.