MALIGNANT TUMOURS IN ANIMALS. 593 



generally, sarcoma grows more rapidly than carcinoma, and although 

 it has less tendency to invade the skin and lymphatic glands, it pro- 

 bably more often becomes generalised in the viscera. One of us 

 reported a case of primary sarcoma of the femur in a large dog, which 

 died in consequence of invasion of the lungs ; on post-mortem examina- 

 tion more than 2000 tumours were counted on the surface of the 

 internal organs. 



Despite the existence of cancer the patient's general condition may 

 remain good. This is particularly the case in cancer of the mammary 

 gland. Distinct wasting may only commence after one or two years. 

 When the lesions become generalised the animals appear weak and 

 depressed, showing a train of symptoms depending on the organs 

 attacked. 



As death approaches the white blood-corpuscles usually increase 

 in number. In the dog just mentioned, the proportion shortly before 

 death was one leucocyte to seventy-three red blood-corpuscles. 



Incomplete ablation of cancerous tumours is always followed by 

 return, the new tumour generally developing more rapidly than the 

 primary. But early and total extirpation seems to give better results 

 than in man. Horses and dogs which had been operated on were 

 under observation for periods of a year, eighteen months, and two 

 years without showing any return. 



To sum up, cancer in animals seems, in a general sense, less grave 

 than in man. It has a greater tendency to remain localised to the 

 point of origin and returns less rapidly and less frequently. But 

 these differences are far from being absolute, and in spite of the 

 reserve with which we have spoken, it must be recognised that in all 

 mammals cancer presents the same anatomical and clinical characters. 



We have sufficiently dwelt on the microscopic appearance of the 

 new growths and shall not therefore return to it. 



We simply add that examination of tumours in animals affords 

 powerful evidence in favour of the epithethelial origin of cancer. 

 It shows that the tumour presents special characters indicating its 

 origin, as we pointed out when speaking of new growths in the mam- 

 mary gland, testicle, and skin, and when describing the case of the 

 horse with a pavement epithelioma developed on the cuticular portion 

 of the gastric mucous membrane. It is also interesting to note that 

 tumours of the mammary gland have a tendency to develop into 

 complex types and to undergo chondroid, or even osteoid, transforma- 

 tion. This tendency is also seen in man, though in an infinitely 

 smaller proportion of cases. 



