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IV. 



MALIGNANT TUMOUES IN BIEDS, WITH OBSEEVATIONS ON 

 THE CHANGES IN THE BLOOD. 



By a. E. METTAM, B.Sc, M.E.C.V.S., M.E.I.A., 

 Principal of the Eoyal Veterinary College of Ireland. 



Plates V., VI. 



Read April 13. Ordered for Publication May 25. Published August 21, 1908. 



The study of malignant tumours entered upon a new phase when Morau and 

 later Jensen announced the discovery of a malignant tumour in mice capable 

 of being grafted into other mice. Later Hanau, Ehrlich, and others showed 

 that the rat was the subject of a sarcoma also capable of being transplanted 

 to other rats. Further Ehrlich and Apolant discovered a tumour of rats 

 which had a mixed structure — a carcinoma and sarcoma in one — and showed 

 that this tumour when inoculated into other rats after some generations lost 

 its carcinomatous characteristics, and became a pure sarcoma. 



In the dog the so-called infective sarcomata developing upon the genital 

 organs is capable of being inoculated to other sound and healthy dogs ; and 

 though its true character as a neoplasm is challenged, still the definitive cause 

 of the new growth has not been demonstrated. 



It having been shown that certain new growths in certain species of 

 animals are capable of inoculation to others of the same species — and quite 

 recently a cancer in a horse has been grafted on to another part of the body 

 of the same animal — a great stimulus has been given to research, and material 

 of a kind suitable for experimental inquiry has been abundantly provided. 

 Moreover, the fact that a certain new growth can be inoculated to other 

 animals allows investigations to be made at all periods of the growth of the 

 tumour, and hence we have gained much information as to the relations 

 existing between the new growths and the tissues of the inoculated animal. 



The cause of a malignant new growth is not known ; but there are many 

 hypotheses to explain it. It has been maintained by numerous investigators 

 that cancer, for instance, is due to a protozoon, a coccidium-like structure 

 being observed in the cells of the tumour. Much controversy has raged 



