310 H. B. ANDERVONT 



any of its hosts. Virologists will recall that a similar condition was eDcoimtered 

 in a mouse colony carrying the virus of lymphocytic choriomeningitis (Traub, 

 1939). 



Further studies established the genetic constitution and age of the hens as 

 important factors in controlling the amount of virus shed in eggs and that the 

 propagation of the virus in infected eggs was dependent largely upon the 

 quantity of virus the egg received from the dam. When progeny of hens, known 

 to be heavy, light, or non-shedders of virus, were observed for the occurrence 

 of visceral lymphomatosis, many progeny of heavy shedders did not develop 

 the disease. This result emphasized that maternal antibodies from infected 

 dams were also deposited in their eggs ( Andre wes, 1939) and protected the 

 chicks during the critical early period after hatching. Neutralizing anti- 

 bodies were found in day-old chicks from eggs of heavy virus- shedding hens, 

 and, following this lead, it was observed that progeny of immunized hens 

 were much more resistant to infection than those hatched by the same hens 

 before they were immunized. Thus, this series of studies led to hopes of 

 practical control measures. 



It is clear that, fifty years after the discovery of the fowl leukoses viruses, 

 one member of the complex is yielding to persistent efforts. Viewed in 

 retrospect, it is surprising so much time was required to arrive at the present 

 state of knowledge, which holds promise of preventive measures for control 

 of the disease. Burmester (1957) explained this in his recent review. There 

 are three forms of chicken lymphomatosis: ocular, neural, and visceral, 

 depending upon the type and location of the predominating lesion, but two 

 or all three forms may be present at the same time in a flock of chickens, or in 

 one member of a flock. In several countries the neural and visceral forms 

 were recognized more than fifty years ago, but during the first thirty years 

 neural lymphomatosis was the predominant type. The visceral form showed a 

 gradual increase in incidence and, coincident with the advent of modern 

 methods of incubation for commercial chicken raising, has become the most 

 prevalent. It also became increasingly apparent that it was far more contagious 

 than the other leukoses and, for this reason, and the fact that it was of 

 economic importance, efforts to control the spread of this disease seemed 

 feasible and received financial support. 



Regardless of the motives for conducting studies with this virus, the results 

 have contributed much to the general problem concerning the tumor viruses. 

 The virus of visceral lymphomatosis is a contagious tumor virus and its 

 transmission by way of water and excreta dispels the idea that tumor viruses 

 have unique and mysterious routes of transmission which enable them to 

 survive and gain access to new hosts. Even transmission via the egg is not an 

 exclusive property of this virus because other disease-provoking agents 

 (Fuller, 1956) are known to be transferred in like manner. It does, however, 



