NEUROLYMPHOMATOSIS 7 



If these birds had not been kept under strict observation with blood counts 

 being made every week, some of them could easily have passed as healthy, 

 since they laid occasionally and appeared to be well. It is possible that myelo- 

 leukosis is spread by traffic in latent cases. 



MONOLEUKOSIS 



One outbreak of monoleukosis has been observed in Massachusetts. In 

 this type of leukosis the blood contains a large number of cells with bean-shaped 

 nuclei. Due to the pressure of other work this disease was studied from a 

 diagnostic point of view only. No other cases have appeared in this laboratory, 

 and it is not known that this disease has ever been reported in poultry before. 



LYMPHOLEUKOSIS 



Lympholeukosis is a form of leukosis in which the lymph system is involved. 

 The pathological cell in lympholeukosis is the lymphoblast. These cells are 

 formed in the lymphoid tissue of the bone marrow, liver, intestines, and cecae 

 (Jordan, 1935; Gibbs and Johnson, 1936). In the fowl the lymphoblast readily 

 migrates into the blood stream, because the vascular system is open. In the 

 early stages it can not always be distinguished from the myeloblast. Whenever 

 lymphoblasts or any other premature cells appear in the blood they are treated 

 as foreign bodies, and an attempt is made by the liver and spleen to remove 

 them. In some cases these organs simply become distended with free cells., 

 while in others the lymphoblasts become invasive and replace the normal liver 

 and spleen cells, forming a neoplasm known as lymphoblastoma. A common 

 form of lymphoblastoma in the fowl is "big liver disease." The cells composing 

 a lymphoblastoma acquire other characteristics in addition to invasiveness, 

 which appear in the chromatin material of the nucleus and may be brought out 

 by special staining methods. They are smaller and more vesicular than the 

 lymphocytes of the blood, and this vesicularity appears to be associated with 

 invasiveness. In eyrthroleukosis and myeloleukosis the liver and spleen may 

 be distended with erythroblasts and myeloblasts. Sometimes these cells are 

 malignant and invade the liver and spleen resulting in the formation of erythro- 

 blastomas and myeloblastomas, but more often they are found filJing the vas- 

 cular spaces and seldom infiltrate extravascular tissues. The type cells com- 

 posing the myeloblastoma contain coarse chromatin in the nucleus with a 

 tendency toward vesicular arrangement. But vesicularity is not the most 

 prominent characteristic of the myeloblastoma cells due to the greater promi- 

 nence of the eosinophilic granules in the cytoplasm. 



Every attempt to transmit lympholeukosis from diseased to healthy birds 

 by means of blood and ground liver failed. An examination of the ground liver 

 smears on slides stained by trypan blue (Evans and Schulemann, 1914), showed 

 that nearly all of the cells had been destroyed. This may explain some of our 

 earlier failures to transmit this disease. 



After considerable trial and error an improved method was found for the 

 transmission of lympholeukosis. The study of field cases revealed large numbers 

 of lymphoblasts in the portal blood (Figure 1), some of which were in mitosis 

 while others presented a vesicular arrangement typical of lymphoblasts. Blood 

 from five spontaneous cases, containing these cells, reproduced the disease 



