TRANSMISSIBLE FOWL LEUKOSIS 17 



immaturity of the erythrocytes and granulocytes and changes of the cellular 

 reticulum of the liver, spleen, and bone marrow as well as proliferative changes of 

 the vascular endothelium in three chickens. 



Troisier (202) studied the transmissibility of 23 cases of spontaneous sarcoma- 

 tosis of the chicken. The neoplasms were transmissible in six of these cases and 

 he believed that in some of these cases the neoplasms were associated with leukosis. 

 This association was, however, not constant and the possibility of spontaneous 

 occurrence of leukosis was not entirely eliminated. 



Troisier and Sifferlen (203) review this work and express the belief that a single 

 agent may be responsible for both sarcoma and leukosis in these experiments. 

 This cannot be generally true as Furth (82) has shown that the agent of pure 

 transmissible erythroblastic leukosis (Strain 1) can be separated from the agent 

 of a fibrosarcoma (Strain 11) when both are inoculated into the same chicken. 

 Furthermore, Furth (81) has submitted evidence to indicate that the mixed 

 osteochondrosarcoma and lymphomatosis producing agent (Strain 12) and the 

 Strain 2 agent are distinctly different, although the Strain 12 agent was derived 

 from a chicken previously inoculated with the Strain 2 agent. 



Mcintosh (140) induced sarcomas in chickens by injections of tar and lard. 

 The tumors thus produced were then transmitted through successive generations. 

 In one series of experiments leukosis was observed to be associated with the disease 

 in its earlier passages, but after the second or third passage the tumor appeared 

 to settle into a single type and the leukotic character disappeared. Mcintosh 

 and Selbie (14l)\describe a further series of transmission experiments with tumors 

 induced in the chicken with tar. In one series the first passage of the induced 

 tumor produced a reaction in one of the inoculated birds which may be con- 

 sidered a form of myelocytoma. The tumor masses in the case of myelocytoma 

 were adjacent to the sternum and ribs and were composed of undifferentiated 

 cells and myelocytes, while the blood from the heart contained many myelo- 

 blasts and myelocytes. There was no evidence of sarcoma in this animal. In the 

 third passage the tumors were composed of a mixture of myeloid and connective 

 tissue elements, and in subsequent passages the tumors were composed of only 

 connective tissue elements. Mcintosh and Selbie believe that there was an 

 association of two agents in these experiments, each responsible for one of the 

 two types of reactions noted. 



Incubation Period and Course 



The incubation period is usually considered as the interval between inoculation 

 and the appearance of immature cells in the blood. The length of this period 

 varies with the different strains. Successive animal passage appears to be an 

 important factor in enhancing the virulence of the agent and thereby shortening 

 the incubation period. Ellermann (41) believed that the increase of virulence 

 of the leukosis agent occasioned by successive animal passage was marked more 

 particularly by a decrease in the length of the course of the disease rather than 

 by the ability to produce disease in a higher percentage of chickens. It has usually 

 been stated that the incubation period and the duration period (interval from the 

 time of first evidence of disease to death) of granuloblastic leukosis are shorter 

 than those of erythroblastic leukosis. Engelbreth-Holm and Rothe Meyer 

 (59), however, report that 1210 chicks affected with erythroblastic leukosis 

 produced by the agents of Strains R, Ti, and E-S lived for an average of 12 days 

 after inoculation, whereas 127 chicks affected with granuloblastic leukosis pro- 

 duced by the agents of strains Ti, 0, and AA lived for an average of 32.5 days. 



