340 Tumors. 



Statistics of Tumors in Animals; Influence of Age and Sex.— It has only 

 been within very recent times that any attempt has been undertaken to 

 systematically collect the material relating to- the frequence of tumor occur- 

 rence in animals (Johne, Frohner, Casper, Sticker). It is very difficult 

 at the present time to draw any comparison of these data with those 

 of man whose tumor involvements have for many years been subjects 

 of careful, conscientious and extensive statistics in literature. The early 

 slaughtering of the food animals is partly at fault, as many tumors are 

 not apt to appear until advancing age. This is especially true of cancer, 

 according to Frohner; which in dogs is not encountered at all for the first 

 two years, and is met with any degree of frequency only in old dogs; 

 eighty-seven per cent, of his animals affected with cancers were over five 

 years of age, fifty-four per cent, over seven years old (in man cancer is 

 most frequent between the fortieth and seventieth year — about seventy per 

 cent.). While in man cancer is of special frequence on the lips, stomach 

 and uterus, in these sites the tumors are very rare in animals (gastric 

 cancer has been observed but one time in the dog— Eberlein). Sarcomata, 

 however, are mainly met in young animals. 



As far as sex may have influence upon tumor formation, it can merely 

 be said that the female sexual apparatus in animals is far less frequently 

 involved by malignant tumors than in mankind; only in the mammary 

 glands of bitches are various tumors to be met with any frequence, while 

 cancers of the genital tract occur only as great rarities. 



As indicative of an influence exerted by the species upon the devel- 

 opment of tumors, it may be stated that cancer is relatively frequent in 

 dogs, melanosarcoma and cancer in horses, and sarcomas in cattle and 

 swine (Casper). 



Resume of Tumors. — The nomenclature and classification of 

 tumors is, as explained on p. 326, mainly dependent upon their his- 

 togenesis, origin and tissue composition. The existence of many 

 types of component tissues, together with the fact that cells of mul- 

 tiplying tissue may present all sorts of shapes, and that sometimes 

 unusual tissues take part in the formation and that it is often im- 

 possible to determine from what normal type of tissue the tumor 

 had its origin, make it difficult to carry out the classification 

 strictly upon this basis. A certain number of tumors present 

 themselves always in the same forms and these can be sharply 

 defined; but there are others which are of mixed structure and 

 of intermediate types. 



The principal types of tumors may be distinguished as fol- 

 lows : 



I — Fibroma^ simple fibrous connective tissue tumor or fibrous 

 tumor. 



2 — Lipoma^ fatty tumor. 



3 — Myxoma, mucoid tumor. 



