TRANSMISSIBLE FOWL LEUKOSIS 27 



174 e). His results were similar with plasma from chickens with both types of 

 disease. He compared his cultures so nourished with those in which he used 

 plasma from normal chickens and observed stimulation of the migration of some 

 immature elements (fibroblasts, polyblasts, and chondroblasts) and inhibition of 

 the more mature blood cells (especially the polymorphonuclears). He suggests 

 that this is due to specific action of the agents of leukosis and sarcoma as no such 

 action was noted in a culture of mouse spleen supplied with plasma from a mouse 

 affected with leukemia. 



Storti and Mezzadra (186) have given a preliminary report on their attempts 

 to cultivate the agent of fowl leukosis in the chorio-allantoic membrane of the 

 chick embryo. They inoculated the fertile eggs which had been incubated for 

 from 4 to 15 days with three to four drops of leukotic material, usually blood. 

 The membranes were removed from the incubator at various time intervals, 

 ground up, and inoculated into the breast muscle of susceptible chickens. Mem- 

 branes from eggs that had been incubated for from 18 hours to 7 days produced 

 the disease. About 75 percent of the membranes which gave positive results 

 showed changes characterized by thickening, opacity, and cornification of the 

 epithelium, together with edema, hemorrhage, hyperemia, and leukocytic in- 

 filtration in the mesenchyme. Infertile eggs were inoculated and incubated as a 

 control measure, but in such eggs the ability to produce disease was lost within 

 48 hours. Van den Berghe and d'Ursel (206 b) report similar successful cultiva- 

 tion of the leukosis agent on the chorio-allantoic membrane of incubated eggs. 



The use of such terms as "destroyed," "perished," "viable," and so forth in 

 the preceding discussion might seem to imply that the substance which induces 

 leukosis in chickens is a living agent, but such a suggestion is not intended. 

 Jarmai, Stenszky, and Parkas (105) suggested that the agent is an enzyme-like 

 product of the leukemic cells themselves which is capable of so altering the cells 

 which it afTects, that it stimulates the newly affected cells to further production 

 of the agent. Jarmai (103) pointed out the marked resistance of the leukosis 

 agent and the agent of transmissible chicken sarcoma to roentgen rays as com- 

 pared to the destruction of tumor-inducing ability of cells of a chemically induced 

 mouse sarcoma and two transmissible mouse carcinomas after exposure to rela- 

 tively small doses of the rays. Engelbreth-Holm and Frederiksen (53) report 

 that the fowl leukosis agent, partially inactivated by oxidation, could be re- 

 activated by a reduction system of cystein-cobalt sulfate, which is suggestive 

 of a non-living state. Engelbreth-HoIm and Rothe Meyer (58) suggest that the 

 term "endogenous agents" might be used to include the agents of fowl leukosis 

 and transmissible fowl sarcomas which they believe are produced in the cells 

 attacked by the agent and are to be regarded as different from the viruses re- 

 sponsible for the more highly contagious diseases. As evidence for the endogenous 

 production of the agent they cite the experiments of Mcintosh (140) in which 

 he induced sarcomas in the chicken with tar and demonstrated the transmission 

 of these tumors with a filter-passing agent. 



Specificity 



The transmissible agent appears to be only relatively specific for Callus domes- 

 ticus. Engelbreth-Holm and Rothe Meyer (54) stated that a temporary state of 

 anemia followed the intravenous administration of leukemic blood in three of 

 eight guinea fowls. Although typical erythroblastic leuko.sis did not develop in 

 the guinea fowls, they believed that this case tended to demonstrate the agent 

 as not being entirely specific for Callus domesticus. They found the pheasant to 



