204 ROUS— AVIAN TUMOR IN ITS RELATION [April .9. 



have been elicited against a normal tissue capable of growth on 

 transplantation (embryonic tissue). 



Taken together the foregoing traits identify the chicken sarcoma 

 as a typical malignant tumor. In them there is nothing to suggest 

 the presence of a parasitic cause for the disease, but much that has 

 been held to favor the view of an intrinsic cell-derangement. 



For the first attempts to separate out the sarcoma's cause filtra- 

 tion was employed. The tissue of a rapidly growing tumor was 

 ground with sand, taken up in Ringer's solution, shaken for some 

 time, centrifugalized, and the supernatant fluid was passed through 

 a Berkefeld filter which held back small bacteria. The injection of 

 a few cubic centimeters of the limpid fluid thus obtained gave rise to 

 the characteristic spindle-celled growth in fowls previously normal; 

 and this growth was capable of further transplantation through an 

 indefinite series of hosts. More recently the causative agent has 

 been dififerentiated from the living tumor cells by drying, by glyceri- 

 nization and by repeated freezing and thawing, — processes which the 

 tumor cells fail to survive. It remains active for many months in 

 dried sarcomatous tissue, and for at least one month in tissue placed 

 in 50 per cent, glycerin. It is quickly rendered innocuous by tem- 

 peratures above 53° C, by 50 per cent, alcohol, by 2 per cent, phenol, 

 by saponin in high dilutions, by chloroform and toluol in the pro- 

 portions which prevent bacterial growth during autolysis, and by 

 autolysis itself. It will not pass through a dialyzing membrane, nor, 

 in our experience, through a porcelain filter. These various features 

 seem sufficient to identify it as a living organism in distinction from 

 a ferment. The organism has never been directly observed in fresh 

 or stained preparations ; and the morphology of the individual 

 tumor cells does not suggest its presence. Attempts to cultivate 

 it in vitro have not as yet proven successful. 



The neoplastic change brought about by the agent takes place 

 slowly compared with the proliferation of the cells, once they have 

 become sarcomatous. Growth of the tumor, dissemination, injury 

 to the host, immune processes, all are referable to these cells sud- 

 denly endowed with new properties. The introduction into a sus- 

 ceptible fowl of a large amount of the filterable agent is not in itself 



