10 MASS. EXPERIMENT STATION BULLETIN 370 



(Undoubtedly these data include lymphocytomas and myelocytomas as well as fowl leukosis, 

 for Kitt made no etiological distinction between these conditions and classified them as a group.) 



A recent report by Goss (90a) on the study of 7408 birds which died among 

 a population of over 24,000 chickens in six different poultry flocks indicates the 

 seriousness of neoplastic disease in the chicken. Tumors were encountered in 

 1445 (19.51 percent) of the birds necropsied. He found that "tumors composed 

 of leucotic cells (both lymphocyte and myelocyte-like cells) accounted for 13.38 

 percent of the losses." 



Jarmai's (99) observations in Hungary are also of interest in this connection: 



Fowl leukosis in its spontaneous form has usually been observed in birds over 

 six months of age and to affect only relatively few individuals of a flock at any 

 given time (Feldman and Olson 63). An unusual situation was encountered by 

 Hamilton and Sawyer (92) in which 35 of a group of 108 chicks 30 days old and 

 18 of 123 chicks 39 days old became affected with the disease within a period of 

 two weeks. 



There appears to be some relationship between the season of the year and the 

 occurrence of the disease. Ellermann (35) stated that in Denmark it appeared 

 more frequently in the first quarter of the year. Kitt (121) and Liittschwager 

 (130) observed it more frequently in the autumn, winter, and spring months in 

 Germany. In Japan it appeared in the late spring (Matsubara 139). Jarmai 

 (97) and Jarmai, Stenszky, and Farkas (105) in Hungary observed the disease 

 more often in the autumn and winter months. It is of interest in this connection 

 that Engelbreth-Holm (52) has pointed out a seasonal variation in the occurrence 

 of acute leukemia in man. Of 95 cases in the Copenhagen hospitals there were 

 twice as many in the winter season as in the summer. The seasonal difference 

 was much more marked in adults than in children. 



TRANSMISSION OF FOWL LEUKOSIS 



The inciting factor or factors which cause fowl leukosis in its spontaneous 

 form are not known in spite of much experimental work. Fowl leukosis seems to 

 occur much more frequently in some breeds of fowls than in others and it ap- 

 parently occurs more frequently in some strains of a breed than in other strains 

 of the same breed (Feldman and Olson 63). Experimental attempts to transmit 



