Part 7

Tyzzer[106] found in a mouse a primary adenocarcinoma of the lung and an adenoma of the kidney. Loeb[107] found that upon the transplantation of a pure gland-like tumor (carcinoma) which originated in the submaxillary gland of a Japanese mouse both carcinoma and spindle cell sarcoma were developed, and this observation, that transplanted tumors may give rise to a different histological growth from that which was transplanted, has been made by others. Tyzzer[108] reports 20 spontaneous tumors in mice. Of these tumors 12 were papillary cyst-adenomas of the lung and were mostly very minute, some of them microscopic; 2 were cyst-adenomas of the kidney; 2 lymphosarcoma, 1 of the groin and 1 of the mediastinum, and 4 were adenocarcinoma. These 20 spontaneous tumors occurred in 16 mice, 4 of them having tumors of 2 different types. Ehrlich and Apolant[109] record the occurrence in a white mouse of a mixed tumor (carcinoma sarcomatodes). Saul[110] mentions spontaneous papillary adenocarcinoma and teleangiectatic carcinoma both in the mammary glands of mice.

Saul showed that by planting the common liver worm of the rat (_Cysticercus fasciolaris_) subcutaneously in a mouse he was able to develop a tumor which partook of the nature of a malignant (carcinomatous) growth. It will be seen by an examination of the data presented below relating to spontaneous tumors in wild rats that a considerable number of them have been associated with the presence of the parasite Saul used in his experiments. He also states[111] that Borrel found worms or their remnants in malignant tumors of mice.

When metastases occur in mouse tumors the most usual seat of the secondary growths is in the lungs, thus Tyzzer[112] observed metastases in 4 cases out of 73 mice inoculated with the Jensen tumor. He demonstrated that the metastases took place by the blood vessels, not by the lymphatic channels, although the tumors were of a carcinomatous nature.

Simon[113], who reviews the subject of mouse tumors with special reference to the subject of immunity, remarks that mouse carcinomata, although found most frequently in old females, when transplanted grows equally well in males, and better in young than in old animals. It has been found by some observers that a rat or a mouse unsuccessfully inoculated with a strain is thereafter immune, to even the most virulent strain.

Haaland[114] and other writers have found a marked variation in the susceptibility of different races of mice to mouse carcinoma.

Ehrlich[115] and his co-workers Apolant and Haaland have recorded many experiments in transplantation of tumors of mice. They have demonstrated that moderate heating of a mouse tumor lengthens the incubation period, diminishes the number of successful transplantations, and brings about certain changes in the histology of the tumors reproduced.

Gay[116] found a difference in the susceptibility of white rats from different sources. In his work with carcinoma in rats he found metastases regularly in the lungs and rarely in the lymph nodes. He was able to raise the virulence of the tumor by transplantation of the lung metastases. This increase of virulence was shown by increase in the rapidity in growth, increase in metastases, and the increase of the epithelial elements over the stroma.

Brooks[117] in considering the subject of tumors in animals concludes that true neoplasms are very rare in wild animals living under natural conditions. It should be stated, however, that Brooks refers especially to higher mammals such as are found in zoological collections.

TUMORS OF WILD RATS.

A new growth is found approximately once in every thousand rats examined in San Francisco. Ninety-two tumors have been examined microscopically. Time has been available for the study of but one or at the most two sections from each tumor and while in some cases the diagnosis was easily made in others there was room for considerable difference of opinion as to the nature of the growth. It is obvious that it is hardly fair to expect to make a final diagnosis in every case from one or two sections taken from one part of the growth, and it is possible that further study will throw more light upon the histological nature of some of them.

_Location._—The largest number of the tumors have been found in the subcutaneous tissue of either the thorax or of the abdomen, and as the majority of these have been found in female rats we have assumed that they were probably of mammary origin. The growths were occasionally located directly under the nipple, but in such cases the nipple was not retracted, and it was exceptional to find any ulceration. The tumors were very rarely adherent to the surrounding tissue. After the subcutaneous tissue tumors were found most frequently in the liver. Histologically, the most of these growths were sarcomas and the majority of them had a parasite, the _Cysticercus fasciolaris_, in some part of the tumor. This parasite, as is well known, is the larval stage of a tapeworm found in the cat. These tumors of the liver were frequently associated with an enormous number of secondary growths varying in size from a millet seed to 1 centimeter in diameter scattered through the omentum, mesentery, and other abdominal structures.

Several growths have been found in the kidney, mostly of an epithelial nature, one being a particularly well-marked example of a cystic papilloma. A few have been found in connection with other parts of the genito-urinary tract. A large bloody tumor, which upon microscopical examination was found to be an angiosarcoma, replaced a testicle. A large growth, apparently an endothelioma, was found near the end of one horn of the bicornuate uterus.

METASTASES.

Metastases have been found in a number of cases of sarcoma and a smaller number of cases of the epithelial growths. Most frequently the secondary tumors were in the liver, the mesentery or the kidney.

_Size._—In proportion to the size of the rat the tumors were quite large, scarcely any under 1 centimeter in diameter having been observed, and they varied from this to a growth several centimeters in diameter.

HISTOLOGICAL STRUCTURE.

The following tumors may be regarded as of the connective tissue type:

LIPOMATA.

One typical lipoma has been found. It was located in the subcutaneous tissue of the thorax and was similar in gross and microscopical appearance to the tumors of the same nature in man.

FIBROMATA.

A considerable number of subcutaneous tumors have been typical hard fibromas, others were fibromas in which there were a few cell nests that led to the suspicion that perhaps a malignant change was taking place in the tumor, or that a malignant growth was being converted into one of a benign nature.

SARCOMATA.

Typical spindle cell sarcomas have been encountered a number of times. A few round cell sarcomas were found in which there were usually a number of giant cells, but hardly enough to justify one in designating the growths as giant cell sarcomas. Several other growths have been seen which gave the impression of being sarcomas but left one in some doubt as to whether the tissue might not be of the nature of a granuloma.

Many tumors of the epithelial type were encountered which may be classed together.

ADENOMATA AND CARCINOMATA.

Several very typical adenomas and cystic adenomas have been found. A few tumors were observed that presented the appearance of carcinomas. A large number of growths were observed that apparently stood between the adenoma and the carcinoma and there was room for legitimate difference of opinion about any one of these, and in fact, different pathologists who have examined sections of these tumors have expressed different opinions as to the nature of the growths.

REFERENCES.

Endnote 101:

Hanau (Fortsch. der Med., vol. 7, 1889, May 1, p. 321).

Endnote 102:

Herzog (Journal Med. Research, 1902, vol. 8, old series, p. 74).

Endnote 103:

Loeb (Journal Med. Research, 1901, vol. 6, p. 28; also vol. 3, p. 44, and vol. 17, p. 299).

Endnote 104:

Flexner and Jobling (Journal Am. Med. Assn., 1907, vol. 48, p. 420).

Endnote 105:

Gaylord and Clowes (Journal Am. Med. Assn., 1907, vol. 48, p. 15).

Endnote 106:

Tyzzer (Journal Am. Med. Assn., 1906, vol. 47, p. 1237).

Endnote 107:

Loeb (Univ. of Pa. Med. Bull., 1907, vol. 19, No. 5).

Endnote 108:

Tyzzer (Journal Med. Research, vol. 17, No. 2, p. 155).

Endnote 109:

Ehrlich and Apolant (Berl. klin. Woch., 1907, vol. 44, pp. 399 and 1401).

Endnote 110:

Saul (Centralblatt für Bact., etc., Aug. 27, 1907, vol. 47).

Endnote 111:

Saul (Centralblatt für Bact., etc., 1909, vol. 49, p. 4).

Endnote 112:

Tyzzer (Journal Med. Research, vol. 17, No. 2, p. 137).

Endnote 113:

Simon (International Clinic, vol. 2, 18th series).

Endnote 114:

Haaland (Berlin, klin. Woch., 1907, vol. 44, p. 73).

Endnote 115:

Ehrlich, Apolant and Haaland (1906, Berlin, klin. Woch., vol. 43, No. 2).

Endnote 116:

Gay (1909, Journal Med. Research, Vol. XX, No. 2).

Endnote 117:

Brooks (1907, Am. Jour. of Med. Sciences, Vol. CXXXIII).

THE ECTOPARASITES OF THE RAT.

By NATHAN BANKS,

_Assistant Entomologist, Bureau of Entomology_.

The ectoparasites of the rat fall naturally into three groups, the fleas, the lice, and the mites. These three groups are widely separated from each other, the mites belonging to the class Arachnida, having four pairs of legs, no segmentation to the body, no antennæ, and no compound eyes. The fleas and lice belong to the class Insecta. The lice are near the order Hemiptera, sucking insects without a complete metamorphosis, while the fleas are related to the Diptera and pass through a complete metamorphosis. All of these three groups, however, agree in one character—they are wingless. The mites and lice have flattened or depressed bodies, while the fleas have compressed bodies. All three groups have many other species which infest various other animals. Few, if any, of these parasites confine themselves to the rat, and all can walk or jump in the adult condition, so that they can easily transfer their attentions from one rat to another or to some other host. The majority of them are known to occur on mice, and several of the fleas and mites will readily attack man.

FLEAS—SIPHONAPTERA.

These wingless, compressed insects are known to all, but few have taken the trouble to look at them with much care. The adult female flea deposits her eggs among the hairs or fur of the host animal, but, unlike the eggs of many parasites, these are not fastened to the hairs and fall freely to the ground. These eggs are oval, whitish, and smooth, and about one-half millimeter long. The larvæ escape from the eggs in two to five days. They are enabled to break the eggshell by a slender process on the top of the head which disappears after the first molt. This larva is a slender, legless, cylindrical creature, whitish or yellowish in color, with a head and 13 segments. There are a few scattered hairs or bristles on the body and at the tip is a pair of corneous processes. On the upper part of the head is a pair of short, slender appendages, the antennæ or feelers. At the front of the head is a pair of biting jaws or mandibles. These larvæ feed on almost any kind of refuse; some have been reared on the sweepings from rooms. There is always some organic matter in this refuse, and this is doubtless their nourishment. The larvæ in houses usually crawl into cracks or under carpets and feed on the dust that occurs in such places. Those that infest wild animals probably feed on the refuse in the nests or retreats of these animals. They remain in the larval stage from a week to ten days, sometimes two weeks, molting the skin three times in this interval. Then they spin flat, white, silken cocoons, in which they transform to the pupal stage. Sometimes the cocoon is covered with particles of dust. In from five to eight days the adult flea emerges from the cocoon. The period of their transformation is affected by the temperature and moisture. In warm, damp weather a generation may develop in ten days or two weeks, but usually about eighteen days to three weeks elapse from the egg to adult. Although some moisture seems necessary to their development, an excess is apt to destroy the larvæ.

[Illustration:

FIG. 6.—Flea, showing the various parts. ]

The leaping ability of adult fleas is familiar to all. No part of the leg is particularly enlarged, so that the jump is made by the entire leg as in the leaf-hopper insects, and not by the hind part of the leg as in grasshoppers and flea-beetles. The size of fleas is not as variable as in many insects. Most are about 2 to 3 millimeters long, while the range is about 1.5 to 6 millimeters. The adult flea has a hard, strongly chitinized body. The head is small, and on each side bears a short jointed antenna, which may repose in a groove or depression. Most species have a small, simple eye, but several forms are normally without eyes. The sides of the head below the antennæ are called the genæ. At the lower front end of the head is the mouth and mouth parts. The latter consist of a pair of triangular maxillæ with jointed maxillary palpi and a beak or proboscis made up of one median and four lateral pieces. The outer pair of lateral pieces is the labrum with the imperfectly jointed labial palpi. They serve as a sheath for the other organs, which are more slender. The inner pair of pieces are considered to be the mandibles and the median piece a labrum or hypopharynx. Others call this piece the unpaired piercing organ, the lingua, or the syringostome. There are other interpretations of the homologies of the mouth parts, but the above is the most generally adopted one. The labrum and the mandibles are roughened and constitute the piercing organs which the flea inserts into the host to tap a blood vessel. On the lower part of the head there is frequently a series or comb of stout spines. Similar spines sometimes occur on the posterior border of the pronotum. These series of spines are called “ctenidia,” and they are of great value in classification. Behind the head are three segments, or zoonites, each bearing a pair of legs. These together form the thorax. The upper surface is called the notum (pronotum, mesonotum, etc.). The sides are the pleura—sometimes “epimera” is used; and the ventral part is the sternum. Each of the thoracic segments has a spiracle, or a breathing pore, on each side. The first segment of the thorax, called the “prothorax,” is shorter than the others, and, as above stated, frequently has a row of ctenidia, or spines, on its posterior border. The next segment is the mesothorax, and the third the metathorax. The metathorax usually has some stout bristles in rows on its pleura, which are enlarged and called “epiphyses,” formerly called “squama aliforme.” The basal one or two segments are sometimes partly covered by the epiphyses or the metathorax. These segments consist of a dorsal plate, or tergite, and a ventral plate, or sternite. Behind the thorax is the abdomen of 9 apparent segments. Seven of these segments have a spiracle or breathing pore on the sides. The last segment, or pygidium, bears the genital organs; in the male certain processes called “claspers” at each side of the genital opening. The anal aperture is at the end of the ninth segment between the dorsal and ventral plates. The claspers have a main curved part, and a slender backward projection called the “manubrium,” and at the apex an articulated clawlike process called “the movable finger.” At the tip of the abdomen of the female there is a short median piece called the “style.” The legs consist of five parts: The coxa, a large basal piece; the trochanter, a minute piece at the end of the coxa; the femur, which is usually slightly swollen in the middle; the tibia, which usually has stout bristles or spines on its posterior side; and the tarsus, which consists of five parts or joints. The basal joint is often the longest, and the comparative lengths of these joints is expressed by a formula, as 60–45–32–18–30. The last, or fifth, joint has been called the “metatarsus,” but this name is better applied to the basal joint. At the tip of the last tarsal joint is a pair of stout claws. The coxæ of legs II and III show a longitudinal suture.

Fleas as a rule prefer certain hosts, but are not as particular in this regard as are many parasites. Those species which are best known are found to attack several hosts, including man. This catholicity of taste is what makes them dangerous parasites, the possible transmitters not only of plague, but also of consumption, leprosy, etc. The fleas are treated by various writers under other names, such as _Aphaniptera_, and _Suctoria_. About 300 species are described, and perhaps as many more will be gathered by collectors. Formerly all fleas were kept in the genus _Pulex_; now they are arranged in many genera, and these genera grouped into families. No less than eight such families are recognized by some authorities on this group. The species that occur on rats belong to three families, which may be separated as follows:

1. Thoracic segments much shortened and constricted; labial palpi apparently not jointed; third joint of antennæ without subjoints; no ctenidia; abdomen of female becomes more or less swollen _Sarcopsyllidæ_

Thoracic segments not shortened nor constricted; labial palpi with joints; third joint of antennæ with several more or less distinct subjoints; ctenidia often present; abdomen of female never distinctly swollen 2

2. Posterior tibial spines in pairs _Pulicidæ_

Posterior tibial spines mostly single and more numerous _Ctenopsyllidæ_

CTENOPSYLLIDÆ.

To this family belongs the _Ctenopsylla musculi_ Dugès.

This was formerly placed in the genus _Typhlopsylla_. The head is rather acute in front and has four ctenidia each side; the eyes are very small; the pronotal comb has 22 spines; each dorsal segment of the body has two rows of hairs; the basal row of smaller hairs. The proportions of joints in the hind tarsus are: 45–25–17–8–14. Length 1.8 to 2.5 millimeters. This species is abundant on rats and mice in Europe and other countries; recently it has been taken in California and Florida on rats and mice.

PULICIDÆ.

This family includes the greater number of fleas. They have been arranged in many genera, six of which have been taken from rats. These are separable as follows:

1. Head without ctenidia; eyes distinct 2

Head and pronotum with ctenidia; last tarsal joint with four pairs of lateral spines 5

2. Pronotum with ctenidia; female with one antepygidial bristle on each side _Hoplopsyllus_.

Pronotum without ctenidia 3

3. Last tarsal joint with four pairs of lateral spines; female with one antepygidial bristle each side 4

Last tarsal joint with five pairs of lateral spines; female with two to five antepygidial bristles each side _Ceratophyllus_.

4. Mesosternite very narrow, without internal rod-like incrassation from the insertion of coxa upward _Pulex_.

Mesosternite with a rod-like internal incrassation from the insertion of coxa upward _Xenopsylla_.

5. Eyes rudimentary; female with two to five antepygidial bristles each side _Neopsylla_.

Eyes distinct; female with but one antepygidial bristle each side _Ctenocephalus_.

_Hoplopsyllus_, one species, described as a _Pulex_.

_Hoplopsyllus anomalus_ Baker.

The mandibles scarcely reach halfway down on the anterior coxæ; upon each are two large spines; the pronotal comb has about nine spines each side; and each abdominal segment has but a single row of bristles. The hind femora have six to eight bristles on the side; the proportions of the joints in the hind tarsus are: 26–16–8–5–13. Color, dark reddish brown. Female, 2.5 millimeters; male, 1.5 millimeters.

Described from a spermophile from Colorado and recorded by Doctor Fox and Professor Doane from _Mus norvegicus_ from California.

_Pulex._—Of this, the typical genus of the family, but one species has been recorded from rats.

_Pulex irritans_ Linn.

The mandibles reach about halfway down on the anterior coxæ; the head is regularly rounded in front; there are no transverse rows of bristles on the vertex, and but one row of bristles on each abdominal tergite. The proportions of the joints in the hind tarsus are, 50–30–18–12–32. Color, usually yellow brown. Male, 1.6 to 2 millimeters; female, 2 to 3.5 millimeters.

This, the human flea, is quite cosmopolitan, but more abundant in warm countries than elsewhere. It occurs on many domestic animals and has frequently been taken from rats in California and elsewhere; it also occurs on skunks.

_Xenopsylla._—This genus includes the following species, formerly placed in the genus _Lœmopsylla_.

_Xenopsylla cheopis_ Rothschild.

The mandibles reach nearly to the end of the anterior coxæ; there are no ctenidia on the head or pronotum; the eyes are distinct; each abdominal tergite has but one row of bristles; the hind femur has a row of about eight bristles; the proportions of the joints in the hind tarsus are as follows: 46–30–16–10–20. Color, light brown. Male, 2.5 to 3.5 millimeters; female, 4 to 5.5 millimeters.

This is a true rat flea, but will readily bite man, and is the species chiefly concerned in transmitting the bubonic plague. It is widely distributed, especially in seaport towns.

_Ceratophyllus._—Fleas of this genus are abundant on many kinds of small mammals, especially rodents. There are a great many species and some are so closely related that it is not easy to identify them. Of the eight species recorded from rats, four have been taken in this country. It is not practicable to tabulate these eight species, but the four that occur in our country may be arranged as follows:

1. Hind tarsal joint II with an apical spine much longer than joint III _acutus_.

Hind tarsal joint II with spines not longer than joint III 2

2. Pronotal comb of about 26 spines _niger_.

Pronotal comb of about 18 or 20 spines _fasciatus_ and _londiniensis_.

_Ceratophyllus niger_ Fox.

This species has the pronotal ctenidia of about 26 spines; there are a few hairs on the inner surface of hind femur; apical spines of second joint of hind tarsus not longer than third joint; three hairs in front of the eye and three in front of these; movable finger of claspers with five slender bristles on the outer edge. Color, very dark brown. Length 3.5 millimeters.

Taken in California from _Mus decumans_ and from man.

_Ceratophyllus acutus_ Baker.

This species is readily known by having a spine at tip of the second joint of hind tarsus longer than the third joint and reaching over onto the fourth joint; the abdominal tergites have each two rows of bristles; the male claspers are very large and long, sickle shaped. Color, pale brown. Length, 3 to 3.5 millimeters.

It was described from a spermophile, but Doctor Fox has taken it once from a rat in California.

_Ceratophyllus fasciatus_ Bosc.

There are 18 or 20 spines in the pronotal comb; there are three bristles in front of eye and in female two, and in male four in front of these; there are three or four hairs on the inner surface of the hind femur; the proportions of joints in the hind tarsus are 50–33–20–11–21. The manubrium of the male claspers is very long and slender, and some of the bristles on the movable finger are as long as the joint. Length, male, 1.8 millimeters; female, 2.5 millimeters.

It has been recorded from California on rats, mice, skunks, and man. It is also common in Europe and elsewhere on rats, mice, and other small animals.

_Ceratophyllus londiniensis_ Rothschild.