TRANSMISSIBLE FOWL LEUKOSIS 9 



fowl paralysis if in fact such an entity exists. Asmundson and Biely (3) and 

 Biely, Palmer and Asmundson (15) presented data which tend to demonstrate 

 an inherent difference in susceptibility or resistance to fowl paralysis and lympho- 

 matous tumors between groups of chickens of different breeding. The experience 

 of Bailing and Warrack (28) was that certain individual females would produce 

 progeny among which there was a relatively high incidence of fowl paralysis and 

 lymphoid tumors irrespective of whether they themselves were affected with the 

 disease and regardless of the sire used. Madsen (131), using as parent stock hens 

 affected with the iritis associated with fowl paralysis, raised two generations of 

 chickens and obtained results which seemed to indicate that the incidence of 

 diseases of these types was less in the progeny. Durant and McDougle (32) have 

 recently reported the experimental production of fowl paralysis by the inoculation 

 with blood from chicks whose parents were affected with the iritis form of the 

 disease. The blood of these chicks appeared to be more capable of inducing the 

 disease at certain times than at others, age apparently being the controlling 

 factor. Only eight of the 22 chicks furnishing blood for the inoculations showed 

 evidence of the disease up to ten months of age. A total of 527 chicks was in- 

 oculated and 507 were held as controls with the result that fowl paralysis (both 

 lesions of the peripheral nerves and iritis) was observed in 17.1 percent of the 

 experimental group and 3.55 percent of the control group. The incidence of 

 tumors and leukosis was found to be low and approximately the same in both 

 groups. 



The possibility that normal birds develop the disease as a result of contact or 

 cohabitation with affected chickens has been considered for many years (Doyle 

 31, Gildow, Williams, and Lampman 89) and this question still awaits definite 

 conclusion. 



It is noteworthy that none of the investigators have been able to enhance the 

 virulence of the causative agents developed by them to the extent that there is 

 an overwhelming majority of successfully inoculated birds as compared to the 

 incidence of spontaneous disease among those used for the purpose of control 

 of the experiment. The lack of good evidence on the mode of spontaneous 

 development after natural exposure to the disease is a serious handicap. Most 

 of those who have worked with the disease express the opinion that it is infectious 

 in nature. However, the actual demonstration of its infectious character by ex- 

 perimental transmission is not yet on a very firm basis. 



INCIDENCE OF FOWL LEUKOSIS 



There are few data available to furnish accurate statistics as to the frequency 

 of occurrence of fowl leukosis, largely because of the different systems of nomen- 

 clature and classifications of this group of diseases used in various laboratories. 

 The diagnosis of fowl leukosis is often made by some pathologists to indicate such 

 conditions as lymphocytoma, fowl paralysis, and myelocytoma. In many lab- 

 oratories established for the sole purpose of furnishing a routine diagnostic 

 service the factor of economy limits the time and effort that may be expended 

 in arriving at a diagnosis. The diagnosis of fowl leukosis should be supported 

 by adequate study of the tissues, especially histological preparations of the bone 

 marrow and other organs noted to be affected, and stained blood smears when 

 it is possible to obtain them. 



Jarmai (99) expressed the belief that fowl leukosis was increasing from year 

 to year. He cited the data of Kitt (121) from observations made in Munich: 



