TRANSMISSIBLE FOWL LEUKOSIS 23 



millimicrons, the particle weight to be 2.6 x 10- ^^ and the "molecular" weight 

 to be 146 X 10^. These characteristics of the fowl leukosis agent resembled very 

 much those of the agent of the Rous chicken sarcoma and also those of a material 

 derived from chicken embryo when treated in a similar manner. Only traces of 

 the macromolecular material could be secured from normal bone marrow under 

 the same conditions. 



Biological Properties 



Ellermann (35) found that the infective agent would remain viable when kept 

 for a week in a refrigerator. Hirschfeld and Jacoby (94) demonstrated the dis- 

 tinction between the causative agents of leukosis and avian tuberculosis by ex- 

 posing a mixture of the leukosis agent and avian tubercle bacilli to ice-box tem- 

 perature for 10 days, after which time the mixture caused only tuberculosis in 

 the inoculated fowls. Jarmai (97), however, was able to produce leukosis with 

 emulsions of organs which had been in the ice box for 10 days. Furth (75) found 

 the infective agent resistant to 14 days of exposure to ice-box temperature (4° C). 

 He also found that it was not inactivated by freezing in liquid air and subsequent 

 thawing. Oberling, Guerin, and Boic (151) stated that their best transfers of 

 leukosis were obtained with leukemic whole blood which had been stored from 

 one to thirty daj's in the ice box. 



The causative agent of fowl leukosis has been shown to be thermolabile by 

 different investigators. In Jarmai's (97) experience, a temperature of 56° C. for 

 a half hour served to destroy the agent. Furth (75) found that when leukemic 

 blood was kept at 37.5° C, the capacity to produce the disease was greatly 

 diminished within seven days and was completely lost after 14 days. Oberling 

 and Guerin (146) stated that material kept for two weeks at a temperature of 

 37° C. was rendered avirulent. Wallbach (211), however, reported that leukotic 

 material would produce disease in 30 percent of inoculated animals after it had 

 been exposed for one hour to 70° C., but that a temperature of 80° C. for one hour 

 completely destroyed the agent. E.xposure for 24 hours at 20° C. reduced the 

 virulence of the agent, and after 24 hours at 40° C. the agent produced disease 

 in only 5 percent of the inoculated chickens. 



Desiccation experiments on leukemic blood conducted by Furth (75) led him 

 to believe that the process of drying would often lessen or completely destroy 

 the infective power of the blood. He found, however, that once dried, the de- 

 terioration of the agent was very slow. In one instance he found that leukemic 

 blood that had been in a dried state for 54 days was still infective. Stubbs (190) 

 reported that dried leukemic blood, sealed in tubes and kept in the ice box for 

 932 days was capable of producing the disease. Wakamatsu (209) found that the 

 infective agent of a leukosis strain, which he had received from Engelbreth-Holm, 

 was avirulent 58 days after being dried. 



Furth (75) observed no decrease in the virulence of leukemic blood which had 

 been preserved in 50 percent glycerin for 104 days as compared with that held 

 in glycerin for 54 days. In either case, however, the incubation period was longer 

 when the disease was inducea with glycerinated material than when correspond- 

 ing amounts of fresh blood were used. Jarmai, Stenszky, and Farkas (105) found 

 the agent viable in material kept in glycerin solution for 45 days, and Jarmai 

 (102) has noted the weakening effect of glycerin as indicated by the prolongation 

 of the incubation period. Oberling and Guerin (146) reported leukemic blood to 

 be infective after being kept in glycerin solution for 150 days. 



The agent of leukosis was not harmed by a three-hour exposure to 0.5 percent 



