TRANSMISSIBLE FOWL LEUKOSIS 13 



producing leukosis but attempts with smaller amounts were unsuccessful. In 

 Furth's experience (74) the successful transmission of the disease with blood 

 plasma ranged from 20 to 28 percent of the fowls injected, whereas cell suspen- 

 sions yielded success in 33 to 71 percent of the fowls injected. Jarmai (97) found 

 that the leukemic cells in a 1:12,000 dilution were still capable of producing the 

 disease. 



Many breeds of domestic chickens have been found to be susceptible to the 

 agent of fowl leukosis. It is not unreasonable to presume that all of the various 

 breeds of Callus domesticus may be artificially infected with transmissible leukosis. 

 Age appears to be one determining factor in the susceptibility of chickens to 

 leukosis. Younger fowls seem to be more susceptible than older ones as indicated 

 by a higher percentage of successful inoculations and a shorter incubation 

 period (Stubbs and Furth 192, Stubbs 189, and Engelbreth-Holm and Rothe 

 Meyer 56, 57). 



Types of Disease Produced 



The majority of investigators have come to agree that the agent of trans- 

 missible fowl leukosis will produce two forms of the disease; namely, erythroblastic 

 leukosis and granuloblastic leukosis. Exception must be made for the production 

 of sarcoma with this agent under special experimental conditions which will be 

 discussed later. It is also quite generally accepted that the inoculation of blood 

 from a fowl ill with erythroblastic leukosis may result in the production of either 

 erythroblastic, granuloblastic, or mixed leukosis. The converse is likewise true; 

 that is, granuloblastic or mixed leukotic blood may produce any of these three 

 types of disease upon inoculation into susceptible birds. Furth (71) reported 

 that in 30 transmission experiments, in which 377 chickens received the trans- 

 missible agent of leukosis, 34 developed myeloid leukosis (granuloblastic leukosis), 

 36 erythroleukosis (erythroblastic leukosis), 25 a mixed leukosis, 6 lymphoid 

 leukosis (lymphocytoma), and 4 myeloma. His control data involved 193 chickens 

 among which were two with lymphoid leukosis (lymphocytoma). Stubbs and 

 Furth (193) utilized two groups of 25 chickens which were housed and cared for 

 under identical conditions. One group was inoculated with blood from two 

 chickens affected with fowl leukosis (one erythroblastic and the other granulo- 

 blastic leukosis), with the result that 13 developed leukosis within four to ten 

 weeks after inoculation. The other group was not inoculated. Lymphocytoma 

 was found in one fowl from each group. None of the birds of the uninoculated 

 group developed leukosis. Olson (155) described three strains of leukosis which 

 had been inoculated into 173 chickens. Of this group 106 or 61.3 percent developed 

 leukosis, 69 having erythroblastic leukosis, 29 granuloblastic leukosis, and 8 

 incipient leukosis. Nyfeldt (142) reported the development of a strain of leukosis 

 in which the granuloblastic form was the usual type of disease produced. The 

 strain originated from a case of spontaneous myeloid (granuloblastic) leukosis. 

 Transmission of the disease was effected by the use of whole leukemic blood. It is 

 of interest to note that of 250 chickens inoculated, 49 died shortly thereafter. 

 No e-Kplanation of these sudden deaths was given and they were not considered 

 in the results of the experiments. Among the remaining 201 birds, leukemic 

 niyeloblastosis (granuloblastic leukosis) developed in 105, and aleukemic myelo- 

 blastosis in 8. In some cases of myeloblastosis, erythroblastic changes were present 

 (mixed leukosis). Nyfeldt was not able to confirm the usually observed higher 

 degree of susceptibility of young chicks to the agent of leukosis with this strain. 



Jarmai's (99) strain of leukosis agent, after the first few passages, always 



