TRANSMISSIBLE FOWL LEUKOSIS 5 



the neoplastic cells, although in many cases the distribution of the cells in the 

 tissues is diffuse. The intestines and mesentery, kidneys, ovary, lungs, heart, 

 adrenals, subcutaneous tissues, and the spleen are locations in which the neo- 

 plastic process may occur. The tumor cells are always situated extravascularly. 

 Changes in the peripheral blood are somewhat difficult to observe, as usually a 

 chicken affected with this disease dies suddenly without visible evidence of 

 disease. Nevertheless, Fenstermacher (64) was able to make monthly observa- 

 tions of the blood of 79 chickens found at the time of death to be affected with 

 lymphocytoma and noted no characteristic change in the blood. Ellermann (43) 

 and Andersen and Bang (2) state that there are no changes of the blood in this 

 disease. Schaaf (175) reported that he observed a few instances of spontaneous 

 leukemic lymphocytoma in which the diagnosis was based on histological study 

 only. 



Lymphocytoma is not uncommon, and might prove to be the most common 

 type of neoplastic disease of the domesticated chicken if we but had the proper 

 data from which reliable information could be gained. Fenstermacher (64) 

 observed an incidence of 15.9 percent cases of lymphocytoma among 494 chickens 

 raised beyond six months of age. It is worthy of note that he found the incidence 

 of disease decreased in the second and third generations of birds derived from 

 this stock. 



There are tumors, occurring rather frequently in the fowl, in which the mor- 

 phology of the cells constituting the mass or masses is such that identification 

 of the type cell is difficult. Jackson (95) discusses this group and gives them the 

 name "mixed cell sarcoma" although he states that this term should not be used 

 without an understanding of the predominating cell which constitutes the tumor 

 in question. The feasibility of using a qualifying term as "histiocytic" or "fibro- 

 blastic" as suggested by him is a point to be considered. There can be no doubt 

 that neoplastic disease of this type (especially "histiocytic sarcoma") has been 

 diagnosed without qualification or distinction as lymphomatosis. Round-celled 

 sarcoma, lymphosarcoma, and mixed cell sarcoma are terms which have been 

 used to indicate this or similar types of neoplastic disease in the chicken (Joest 

 and Ernesti 106, Pentimalli 164, Eber and Kriegbaum 33, Eber and Malke 34, 

 F0lger 66, and others). The characteristics of these neoplasms as well as their 

 probable derivation from a cell similar to that which gives origin to the cells 

 of a lymphocytoma are reasons for the tentative linking together of these diseases. 

 The name "atypical lymphocytoma" has been used in referring to this type of 

 reaction (such a case is described in a report by Olson and Dukes, 157), which, 

 although a somewhat ambiguous term, expresses a certain relationship to the 

 more clearly defined disease of lymphocytoma. 



A condition of "lymphoblastoma" has been described by Adamstone (1) as 

 occurring in young chicks fed a diet treated with ferric chloride to destroy vitamin 

 E. The condition described by him is dissimilar to lymphocytoma or atypical 

 lymphocytoma and its exact nature is difficult to determine, although Jungherr 

 (116) has suggested that it may be of an inflammatory character. 



Jungherr (114) and Jungherr and Landauer (117) described a condition of 

 osteopetrosis which they found transmissible and sometimes associated with 

 lymphocytoma-like reactions. Other workers have encountered this condition 

 so infrequently that no further mention of it will be made in this discussion. 



Failures to transmit lymphocytoma by experimental inoculation have been 

 reported by Andersen and Bang (2), Mathews and Walkey (138), Engelbreth- 

 Holm (47, 48, 50), and Fenstermacher (64). Some workers claim to have trans- 

 mitted this disease successfully and believe that there is a common etiologic 



