112 PBINOrPLES OF YETEBINABY SUEGEBY 



years old, the vast majority having been met with in the dog 

 five years and older. In the horse they are also more 

 frequently seen in the older animal. 



2. Food and hereditary tendency are claimed by some to 

 be of etiological moment, it occurring especially in carnivora 

 and rarely in herbivora. These two points seem of very 

 doubtful value. 



3. Irritations. I do not believe that irritations either 

 traumatic or chemic are the direct causes ; they simply pre- 

 dispose. Experiments made upon animals by exposing them 

 to continuous irritation have failed to produce carcinomata. 

 Furthermore, carcinomata are found in parts which are not 

 exposed to irritations, as the thyroid gland, mucous mem- 

 branes of the head, etc. Cancer of the lip and tongue, places 

 certainly exposed to decided irritation, for instance, in the 

 horse, according to this theory ought to be frequent, but, on 

 the contrary, they are very rare indeed. 



4. Parasitic infection. All the various bacteria and 

 coccidia ,so far named as etiological factors, on further 

 experimentation have proved to be saprophytes, and in the 

 case of protozooa and coccidia proved to be no coccidia at all, 

 but degenerative changes of the epithelial cell, their nuclei 

 or nucleoli. In defense of this parasitic theory it is stated that 

 cancer has beeji produced by artificial inoculation. But since 

 m.ost of the inoculation experiments turned out negative, this 

 theory also needs further support. 



5. Oohnheim's inclusion theory also fails to explain the 

 development of most carcinomata, and is only applicable in 

 those cases so rarely met with, primary carcinoma of bone or 

 lymph glands. 



In which animals are carcinomata mainly seen ? 

 Horse, dog and cat. 



