CHAPTER V. 
TUMORS. 
The etiology and pathogeny of tumors are still more obscure in the 
case of animals than in the case of man. The influence of heredity, ad- 
mitted to-day almost without question by numerous and well-observed facts 
for carcinoma of man, seems also established for the other malignant 
tumors. Transmitted neoplastic diathesis may, however, give rise among 
offspring to neoplasms of the same nature as those developed in the 
parents, or of a different type. We have watched a slut operated upon 
twice a year apart, for cancer of the mamme; her two daughters had a 
mammary tumor, one at four, the other at five years old. But few cases of 
this kind have been published, evidently because the previous and special 
clinical history of our patient is difficult to obtain and generally incomplete. 
Species has an undoubted influence. Although, indeed, all animals are 
subject to tumors, they are not subject to them with like frequency. 
Carnivorous animals and solipeds have them more commonly than rumi- 
nants; in certain species (dogs in particular) females are more exposed 
than males by the great proportion of 60 per cent. of the mammary 
tumors in females. Age plays an important part as predisposing cause. 
One hundred observations gathered by us of tumors in dogs are classified, 
according to age, as follows: Below three years, 6; from three to five 
years, 18; from six to nine, 33; from nine to twelve, 26; from twelve 
to fifteen, 14; from fifteen to twenty, 3. Therefore tumors are frequent 
in old animals, rarer in those of middle life ; exceptional in young animals. 
But as each age has its diseases, it has also its tumors; in young sub- 
jects, benignant tumors are almost the only ones observed (polypi, papil- 
lomata) ; sarcoma is seen in adults and in all species, but carcinoma is 
certainly the neoplasm of the old. 
It seems, also, that hygienic conditions to which animals are submitted, 
the régime especially, has an influence on the genesis of tumors. As 
Leblanc remarked, dogs that are fed on meat and deprived of exercise, 
kept tied up or indoors, are oftener affected with tumors than others. 
But it is useless to say that one can at will produce cancers in certain 
species by imposing upon them a special régéme and mode of living; such 
an assertion rests upon no carefully established fact. 
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