TRANSMISSIBLE FOWL LEUKOSIS 29 



at two later intervals, each episode being separated by a period of remission. 

 The chicken died three and a half months after inoculation with "diphtheria" 

 and tuberculosis, at which time a small mass was found at the site of inoculation. 

 The histological appearance of the mass was similar to that of the original material 

 from which the inoculum was prepared. Serial passage of this process and elimina- 

 tion of the possibility that this might represent a granulomatous process would 

 have made more plausible the conclusion of Schirrmeister that this was trans- 

 mission of leukosis from one species of fowl to another. 



^ The modification of the species specificity of the agent causing transmissible 

 fowl leukosis is indeed interesting. As has been mentioned, the majority of 

 strains of this disease have failed to show any effect in turkeys, guinea fowls, and 

 pheasants. The varied degrees of virulence of the different strains may well 

 account for the difference in the results obtained by various workers in their 

 attempts to infect these kinds of fowl. Neoplastic diseases similar to lympho- 

 cytoma of chickens have been noted in many species of fowl (canary, pigeon, 

 duck, goose, and turkey (Richter, 169), but in none of these species -has the 

 disease been demonstrated to be transmissible. 



Jarmai (103 a) has reported the spontaneous occurrence of leukosis and sar- 

 coma in a small parrakeet (Melopsittacus undulans). The bird had a small spindle- 

 cell sarcoma in the subcutis of each wing and the blood and organ changes were 

 characteristic of erythroblastic leukosis. Jarmai injected emulsions of the organs 

 of this bird and minced tumor fragments into other parrakeets (of similar but 

 not identical type), canaries, chickens, pigeons, and mice without positive results 

 in any species. 



IMMUNITY 



Fowls resistant to the transmissible agent of leukosis have been encountered 

 in the experiments of all investigators of the disease. This resistance does not 

 appear to be absolute, as chickens which withstand the first inoculation may 

 succumb to subsequent inoculation (Ellermann 37, Rothe Meyer and Engelbreth- 

 Holm 171, and Engelbreth-Holm 48). Greppin (91) noted 10 resistant birds in 

 his work with the leukosis strain of Oberling and Guerin; all succumbed to the 

 disease after the fifth or sixth inoculation. Rothe Meyer, Engelbreth-Holm, and 

 Uhl (174) state that such naturally resistant birds are not uncommon among 

 adult chickens, but that they have never found such resistance in a chick less 

 than two months of age. It has been the general experience that a greater number 

 of resistant birds have been encountered in the first few passages of a new strain 

 of the disease agent and it is possible that the natural resistance of the experimental 

 birds used in the later passages of the agent is overcome by an enhanced virulence 

 acquired by repeated animal passage. 



Spontaneously recovered birds seem to possess some degree of resistance to 

 subsequent inoculation with the agent of leukosis (Jarmai, Stenszky, and Farkas 

 105, Furth 76, Rothe Meyer and Engelbreth-Holm 171, and Greppin 91). Eller- 

 mann (36) noted that fowls spontaneoush' recovered from the disease were sus- 

 ceptible to further inoculation. Rothe Meyer, Engelbreth-Holm, and Uhl (174) 

 observed one spontaneously recovered bird to be refractory to nine subsequent 

 inoculations with agent-containing material; however, the tenth inoculation 

 resulted in the development of typical erythroblastic leukosis 25 days after its 

 administration. Furth's experiments (76) indicated that the spontaneously 

 recovered chickens were more likely to become affected if the subsequent inocula- 

 tion was made with cell-containing material rather than leukotic material free 

 of cells. 



