TRANSMISSIBLE FOWL LEUKOSIS 7 



paralysis and only moderately elevated in birds affected with leukosis produced 

 by the Strain 2 agent of Furth. 



Myelocytoma 



Synonyms: leukochloroma (Mathews 137), aleukemic myelosis (Ellermann 

 38), aleukemic myeloblastosis (Nyfeldt 142), and myeloma. 



This disease in the chicken was first described by Ellermann (38), who termed 

 the condition "aleukemic myelosis" and believed it to be caused by the filtrable 

 agent of transmissible fowl leukosis. Mathews (137) described the disease and 

 gave it the name "leukochloroma," deriving this term from human pathology. 



Myelocytoma is a neoplastic disease of the fowl in which the myelocyte is the 

 type cell. The tumor has a characteristic appearance. It is devoid of pigment, 

 has a chalky white color, and is very soft. The neoplastic masses are usually 

 found associated with the periosteum of the sternum, ribs, and vertebrae and 

 somewhat concentrated at the junction of the costal and sternal ribs. Soft struc- 

 tures in which foci of myelocytoma have been described are the liver, spleen, 

 ovary, kidneys, heart, intestine, pancreas, thymus, and occasionally the lungs, 

 sciatic nerves, esophagus, trachea, and thyroid gland. The cells of a myelocytoma 

 may be readily studied in imprint preparations.^ Polychrome myelocytes as well 

 as myelocytes may be found in imprint preparations of a myelocytoma. The 

 myelocytes have granules which are round and acidophilic. The polychrome 

 myelocytes possess both acidophilic granules and basic staining preacidophilic 

 granules in their cytoplasm. The nuclei of these cells are usually round or slightly 

 indented and have a finer chromatin and parachromatin arrangement than 

 is found in either the mature heterophil or eosinophil of the blood. Although 

 Jackson (95) calls attention to the fact that these cells may be morphologically 

 identical with the myelocytes of the bone marrow, which normally develop into 

 the blood heterophil with spindle-shaped granules in the cytoplasm, their identity 

 cannot yet be considered settled as knowledge of the relationships between the 

 various blood cells in the tissues of the chicken is not yet complete. It is con- 

 ceivable that these cells might be derived from the tissue histiocyte. 



In some instances, this disease is accompanied by an increase of heterophils 

 and circulating myelocytes in the blood. These circulating myelocytes are 

 indistinguishable from those found in the neoplastic deposits. It would be possible 

 to arrange a series of cases presenting the varying gradations from an instance of 

 myelocytoma in which the blood is normal to the frankly leukemic condition of 

 granuloblastic leukosis. 



Mathews (137) attempted transmission of the disease to 23 experimental 

 chickens. His material for inoculation was derived from three spontaneous 

 cases of the disease and was introduced intraperitoneally, subcutaneously, sub- 

 periosteally, and orally. In no instance did the disease occur in the inoculated 

 animals. Furth (77) observed instances of the disease in fowls inoculated with 

 his Strain 2 agent. 



Fowl Paralysis 



Synonyms of this condition are: polyneuritis (Marek 136), neuritis (Doyle 30), 

 fowl paralysis (Warrack and Calling 214), range paralysis or "leukosis" (Patter- 



^These are made immediately after death of an affected bird by lightly touching a bit of the 

 tumor tissue against the surface of a clean slide. The imprint is dried in the air and then stained 

 with the usual blood stains, more or less concentrated according to the density of the imprint. 



