312 H. B. ANDERVONT 



chicks were most susceptible to the virus of myeloblastosis and resistance 

 increased with age, whereas the converse is true for the erythroblastosis virus, 

 which is far more lethal for 77-day-old than for 3-day-old chickens. Chemical 

 studies revealed that the virus of myeloblastosis showed a pronounced 

 activity to dephosphorylate adenosine triphosphate but the virus of erythro- 

 blastosis was lacking in such activity. 



Serological studies, however, in common with earlier efforts, suggested a 

 strong relationship between the viruses. Sera from chickens actively immun- 

 ized against either virus neutralized both viruses. Of interest was the finding 

 that rabbits injected with myeloblastosis virus or normal chicken tissues 

 developed neutralizing antibodies for both viruses. These results were 

 interpreted as evidence of similar antigens in the viruses. A difference in 

 antigen components was suggested by the observation that the administra- 

 tion of guinea pig kidney tissue to rabbits produced antibodies capable of 

 neutralizing the myeloblastosis virus but incapable of neutralizing the virus 

 of erythroblastosis. Beard interpreted these results as suggesting: (1) a 

 similar antigenic component in the viruses; (2) a second antigenic component 

 intrinsic to both viruses that was derived from, or associated with, normal 

 chicken tissues; (3) a third component, presumably the Forssman antigen, 

 associated with the myeloblastosis virus but not with the erythroblastosis 

 virus. Thus, despite biological and enzymatic differences, serological tests 

 indicate a close relationship between the two viruses. 



Burmester (1957) observed a difference between the neural and visceral 

 forms of lymphomatosis. During the course of investigations in which the 

 egg-borne transfer of visceral lymphomatosis was established, he noted, 

 "only visceral lymphomatosis occurred to any significant extent hi the test 

 chicks inoculated." This finding, together with other negative data on egg 

 transmission of the neural form, was interpreted by Burmester us indicating 

 different causative agents for the two diseases. Apparently, cross-neutraliza- 

 tion experiments between sera from fowls actively immunized against the 

 neural, and visceral forms have not been performed, but Beard (1957) 

 reported that the sera of chickens immunized against the myeloblastosis virus 

 contained neutralizing antibodies for the virus of visceral lymphomatosis. 



This brings us to the point where the fowl tumor complex can be enlarged 

 to include not only the leukoses but other virus-induced connective tissue 

 tumors of fowls. Oberling and Guerin (1954), as well as Duran-Reynals 

 (1953), have reviewed and discussed adequately the evidence for the concept 

 of a group of related viruses acting as causative agents for a variety of fowl 

 tumors. Serological studies revealed natural antibodies to a number of 

 sarcomas in adult chickens, in chicks, and in the egg yolk, while cross- 

 neutralization tests between sera from actively immunized chickens or 

 pheasants revealed definite relationships between the viruses. These findings 



