22 MASS. EXPERIMENT STATION BULLETIN 370 



and similar type tumors exert their effect on the cells of the fibroblastic series. 

 Jarniai (100) explains the action of his strain of leukosis agent, which produced 

 sarcoma after having produced only erythroblastic leukosis for years, by endowing 

 the agent with a predominant hemotropic tendency and also a histiotropic 

 tendency that was subdued by the usual intravenous mode of inoculation. Such 

 a combination of properties is not found in all pure strains of agent causing ery- 

 throblastic leukosis, as was indicated by the failure of Stubbs (191) to induce 

 sarcoma formation. Stubbs injected leukotic blood of Strain 1 into the muscles 

 of a large series of experimental chickens, with erythroblastic leukosis as the 

 only result. 



The work of Jordan (112), indicating that the small lymphocyte of avian blood 

 or bone marrow may be a potential hemoblast giving rise to any of the blood cells 

 in a strictly monophyletic manner, may explain the mode of action of Furth's 

 Strain 2 agent in producing lymphomatosis. From this point of view, however, 

 one cannot readily explain the lack of lymphomatous reactions in the other 

 leukosis-sarcoma strains reported. 



THE TRANSMISSIBLE AGENT 

 Filtrability 



Ellermann and Bang's (45) discovery that the etiologic agent of transmissible 

 leukosis could pass through filters impervious to bacteria has been confirmed 

 by many investigators among whom are Hirschfeld and Jacoby (94), Andersen 

 and Bang (2), Battaglia and Leinati (6), Jarmai (97), Furth and his collaborators 

 (71, 83, 85), and Oberling and Guerin (146). The experience of Ellermann (35) 

 was that the filtrate would infect 16 percent of the chickens inoculated with it. 

 Andersen and Bang (2) reported that 25 percent of chickens inoculated with 

 filtered material would develop the disease. Jarmai (97) observed that 10 percent 

 and Furth (71) that 12.7 percent of birds inoculated with filtrates became leukotic. 

 According to Furth and Miller (85) the inciting agent will readily pass through 

 all types of silicious filters. They found that the incubation period of the disease 

 was somewhat longer when it was produced by filtrates than when it was pro- 

 duced by un filtered material. By filtration through collodion membranes the 

 agent has been shown to be of about the same size as bacteriophage and smaller 

 than 250 millimicrons (Furth and Miller 85). Although Jarmai, Stenszky, and 

 Farkas (105) were unable to pass the agent through a relatively coarse Berkefeld 

 filter, they did pass it through a Zsigmondy-Bachman membrane filter of a pore 

 size which permitted the passage of egg albumin (20 to 100 millimicrons). Johnson 

 and Bell (110) reported that the leukosis agent was found to pass through mem- 

 branes whose pore size was between 100 and 400 millimicrons although these 

 workers extend the conditions caused by the filtered agent to include lymphocytoma 

 and fowl paralysis. 



Stern and Kirschbaum (182) have studied the sedimentation rate and physico- 

 chemical properties of Furth's Strain 1 leukosis agent which had been purified 

 by repeated slow- and high-speed centrifuga'tion in an air-driven centrifuge. The 

 agent was obtained from the bone marrow which was a rich source of the macro- 

 molecular material with which they were dealing. One gram of bone marrow 

 yielded 11 milligrams of macromolecular material. This material was found to 

 produce the disease in four of 19 chickens into which it was inoculated. The 

 macromolecular material was found to contain 9.5 percent nitrogen, to give 

 positive tests for thymonucleic acid, and hemin, and to possess cytochrome 

 oxidase and catalase activity. The size of the agent was estimated to be 72 



