■9-12] TO THE TUMOR PROBLEM. 205 



sufficient to cause a tumor. The development of a growth under 

 these circumstances is conditional upon the presence of a cell- 

 derangement, such, for example, as is produced by the injection of 

 infusorial earth. Yet even when the element of cell-derangement 

 has been supplied, and the agent injected in quantity, a consider- 

 able percentage of the fowls fail to develop a sarcoma. The nature 

 of the factors responsible for this failure has not been determined. 

 The importance of cell-derangement as a contributory cause of 

 human sarcomata has long been recognized. 



The chicken sarcoma is strikingly non-infective under ordinary 

 conditions. During the last three years more than a thousand fowls, 

 with or without the tumor, have been kept together in close quarters, 

 yet no instance of natural transmission has been observed. An 

 examination of numerous spontaneous chicken tumors from various 

 sources has shown that the sarcoma is not epidemic. These facts 

 find an explanation in the various factors by which the agent's action 

 is conditioned. 



In conclusion it should be stated that the experiments with the 

 chicken sarcoma have not yielded a method whereby a causative 

 agent can be separated from the tumors of rats and mice. But they 

 clearly prove that the characteristics of malignant tumors in general 

 are compatible with the presence of a living causative agent. Such 

 a cause for them seems, indeed, far from improbable. 



Note: Dr. James B. Murphy has shared, as joint author, in the 

 work on the chicken sarcoma since the recognition of the latter's 

 filterable cause; and more recently Dr. W. H. Tytler has aided in 

 the study of some of the growth's problems. 



Laboratory of the Rockefeller Institute for Medical Research, 

 New York. 



PROC. AMER. PHIL. SOC, LI. 205 K, PRINTED JULY 24, I9I2. 



