who have investigated this subject are unanimous in asserting that epithelioma of the penis in horses and bulls is exceedingly rare. A specimen of secondary glandular carcinoma of the neck in a chicken has recently come into the writer's possession. The histological

1

FIG. 21.-Secondary glandular carcinoma of the neck of a chicken, X 200: a, epithelial nests; b, vessels.

structure of the tumor, as shown in Fig. 21, is very similar as in the same organ in man. Wild animals in a state of nature and those living in confinement appear to be absolutely free from cancer.

Adenomata occur in domestic mammals. The bitch is especially liable to tumors of the mammary gland that are analogous to the large

cystic adenomata of women. These tumors often attain an enormous size. Large cystic adenomata with intracystic processes are occasionally seen in the udders of cows. The mammary glands of cats are

liable to a disease histologically identical with mammary cancer in women, but cancer such as attacks the human mamma is unknown in cows, mares, ewes, goats, or bitches. Dogs are subject to ulcerating sebaceous adenoma in the skin around the anus, the tumor being prone to return after extirpation.

Teratomata are common enough among domestic animals, and many examples have been described in fish, frogs and other batrachians, lizards, snakes, birds, rabbits, etc.

Cystic Tumors.-The frequency of these tumors in vertebrata generally forms a striking contrast to the infrequency of connective-tissue and epithelial tumors. While true cystic tumors are rare, cystic tumors resulting from retention of a physiological secretion are frequently met with. Such conditions as hydronephrosis, congenital cystic kidney, and dilatations of the vitello-intestinal duct have been observed. Hydrocele of the tunica vaginalis is rare, because the funicular pouch in mammals retains its connection with the general peritoneal cavity throughout life. Cysts arising in connection with the central nervous system have been observed in foals, pigs, and calves. Hydrocephalus is fairly frequent, but spina bifida is rare. Esophageal diverticulæ are often seen in horses, and the same animal is exceedingly liable to synovial cysts and ganglia.

VI. ETIOLOGY OF TUMORS.

In the first section the writer made an attempt to prove, so far as present knowledge of this subject will permit, that all tumors, benign and malignant, have their origin from a matrix of embryonic cells of a congenital or post-natal origin. It remains to discuss here the influences which enable the latent cells to assume active tissue-proliferation, upon which depends the production of tumor-tissue. We regard the matrix of embryonic cells as the essential cause of tumor-formation, without which all intrinsic and external exciting causes are inadequate to produce a true tumor. On the contrary, we must admit that such a matrix will remain harmless in the absence of congenital or post-natal exciting causes. Certain cells never become specialized to a high degree, and consequently retain their original inherent power of proliferation. Before discussing the influence of heredity and post-natal exciting causes reference will be made very briefly to congenital tumors.

Congenital Tumors. In a certain sense the majority of tumors are congenital in so far as the essential matrix of embryonic cells is concerned. It is only in cases in which a tumor develops from a matrix of embryonic cells of post-natal origin that the essential tumor-matrix is not congenital. When we speak of a congenital tumor, however, we mean a tumor which is present at the time of birth. In such cases the tumor-matrix is acted upon during intra-uterine life by influences which determine tumor-formation, and the resulting product behaves clinically after birth in the same manner as do tumors of post-natal origin. We must therefore make a distinction between a true tumor and localized hypertrophy or giant growth at the time of birth. There are in children cases of “partial obesity ”—cases in which the adipose tissue of a certain region of the body is greatly in excess of the adipose tissue generally, and yet the characters of a tumor are wanting. Of such a nature is the case related by Lebert, of a female aged nineteen, the left side of whose abdomen was the seat of an enormous increase of fat. This growth began at the age of six months, and was thought to have been congenital; it grew in proportion to the rest of the body, and ceased to grow when the girl attained puberty. Lebert calls this a “lipoma diffusum." In giant growth the tissues are under the influence of, and are controlled by, the same physiological laws which govern the growth and development of the remaining tissues of the body, while a congenital tumor recognizes and obeys no such governing influences. Angiomata are nearly always congenital. The tumors, although pres

ent at birth, are often overlooked, owing to their small size. Next in frequency as congenital tumors are the lipomata and cysts. Nearly all benign tumors may have a congenital origin. Only in very rare instances have malignant tumors been found and recognized as such at the time of birth. Cases of sarcoma in the cutis of the newlyborn have been reported by Jacobi, Karewski, Ramdohr, Mundillon, L. W. Marshall, K. King, Senftleben Weinlechner, and several others. Ramdohr has reported a case of congenital multiple angiosarcoma. The body of the child, which died shortly after birth, showed a large angio-sarcoma in the region of the chin, and twenty-one secondary superficial tumors; also sixteen metastatic tumors of the various internal organs. Ahlfeld reports a case of congenital fibro-sarcoma of the genital organs in a child three and a half years of age, and a case of congenital carcinoma in the distal end of an atresic rectum in a new-born infant. It is a significant fact that many tumors arise from rudimentary organs, vestiges (Sutton), or accessory organs-" rests" (Sutton) which remain functionless in the body until the time of puberty, when they become the starting-point of a tumor. Tumors from such structures seldom form during intra-uterine life, but appear later. Different forms of retention-cysts have been found in infants at the time of birth. The mechanical obstruction causing the retention is more often the result of a faulty development of the ducts of secreting organs than of other intra-uterine pathological conditions.

Heredity. Heredity in the etiology of tumors is a subject upon which much has been said and written. We no longer speak of a "tumor-dyscrasia," but we cannot ignore the influence of heredity in the origin and growth of tumors. The laws of heredity depend upon the persistence of impressions (unconscious memory) in protoplasm (Williams); hence every living thing produces new ones, each after its own kind. It is by virtue of this property that, in the words of Sir James Paget, "a mark once made in a particle of blood or tissue is not for years effaced from its successors." All are willing to admit that there is a difference in the susceptibility to disease among different individuals placed under the same conditions. Every military surgeon knows that if a body of troops is quartered in a cold, damp garrison, some will be attacked by catarrhal affections of different organs, others will suffer from rheumatism, while the greater number will retain their health after having been exposed to the same morbid influences. We must admit that a similar inherent susceptibility to tumor-formation exists among different persons, and that such individual predisposition is often the result of hereditary influences. Benign tumors are hereditary in the same sense as monstrosities-per excessum. Supernumerary toes

and fingers have appeared through several generations in the same family. The same can be said of most of the non-malignant tumors, particularly angioma and lipoma. Very frequently such tumors were not only hereditary, but also occupied the same localities. Paget found carcinoma of the uterus in three generations-grandmother, mother, and daughter. The writer has repeatedly met with carcinoma of the breast in two successive generations. Sibley relates an instance of carcinoma of the uterus affecting a mother and her five daughters. Warren observed a cancer of the lip in the father; in one son and two daughters cancer of the breast; and in two grandchildren cancer of the breast. The most interesting instance of hereditary predisposition to carcinoma is reported by Broca :

First generation: Madame Z. died of cancer of the breast in 1788, aged 60.
Second generation: four married daughters:

A. Cancer of the liver, 62 years old, 1820.

The fifth daughter escaped the disease.

Madame C. had five daughters and two sons:

The sons remained free from cancer.

The first daughter died of cancer of the breast in 1837, 37 years old.

Of her five children, one daughter died in 1854, of cancer of the breast, at the age

of 49.

The second daughter died in 1822, 40 years old, of cancer of the breast.

From these and other reliable observations it is evident that a predisposition to cancer may be derived by inheritance. Paget collected the histories of 322 cancerous patients with special reference to this point. Of this number, there were seventy-eight, or nearly one-fourth, who were aware of cancer in other members of their families. The proportion is much larger than could be due to chance, and its import is corroborated by the fact of many members of the same family being in some instances affected. It is evident that where a tumor is inherited the two essential causes are transmitted from parent to child: 1. A matrix of embryonic cells; 2. A lack of resistance on the part of the whole