NEOPLASTIC DISEASES IN CHICKENS 5 



some exceptions will be apparent upon examination of the list. The terms 

 "neurogenic sarcoma" and "carcinosarcoma" are specific examples and their 

 use is discussed in the sections dealing with those tumors. 



Some discrepancy may be noted in the relative space allotted for the descrip- 

 tion and discussion of the different types of neoplasms. Justification for this 

 apparent overemphasis of certain t\pes of less common tumors may be sought 

 in the fact that the study has added relatively more to our fund of information 

 concerning these particular types. 



DESCRIPTION OF SPECIFIC FORMS OF NEOPLASIA OBSERVED 



Lymphocytoma 



Comments and Classification 



More than half (213) of the cases in the collection fell into the classification 

 of lymphocytoma. Such a high frequency for this type of tumor in chickens is 

 not surprising. Despite the fact that lymphocytoma is such a common form of 

 neoplasia, however, there has been no satisfactory method or criterion offered 

 for separating the different manifestations of the disease. Some cases are asso- 

 ciated with lesions of the nervous system; some cases have a diffuse distribution 

 of the neoplastic lymphoid cells; and in other cases the foci of neoplasia are 

 nodular. 



For the purpose of study, the cases of hmphocytoma were separated into 

 groups with particular emphasis on the characteristic behavior of the neoplastic 

 tissue as observed from both gross and microscopic examination. Minute cyto- 

 logical details such as the size of the lymphoid cells, the ratio betw^een size of 

 nucleus and size of cell, and the relative num.ber of mitotic figures were not consid- 

 ered in the subdivision of the lymphocytomas although these features were taken 

 into account at the time the individual cases were designated as lymphocytoma. 

 The degree of involvement of the various organs or tissues was classified in four 

 grades at the time of histological examination. In Grade 1 the tumor was con- 

 fined to a few areas; in Grade 2, there were several areas of neoplasia; in Grade 3, 

 a moderate amount of parenchyma was replaced by tumor cells; and in Grade 4, 

 the majority of parenchyma of an organ or tissue was overgrown or displaced by 

 the tumor. Classification of degree of involvement of such tissues as the mus- 

 culature, skin and subcutis, and peritoneum was based on the local invasiveness 

 at the site of the tumor. Such a procedure is not necessarily recommended for 

 routine classification of lymphocytomas. 



A preliminary survey indicated that the lymphocytomas could be separated 

 on the basis of their morphological characters into six groups according to the 

 following scheme: 



Those with nerve tissue involved 

 L Diffuse lymphocytoma 



2. Nodular lymphocytoma 



3. Combined diffuse and nodular lymphocytoma 



Those with no nerve tissue involved 



4. Diffuse lymphocytoma 



5. Nodular lymphocytoma 



6. Combined diffuse and nodular lymphocytoma 



Diffuse Lymphocytoma. — The common characteristic of the group classified 

 as diffuse hmphocvtoma was a diffuse infiltration of the involved organ or tis- 

 sues with neoplastic lymphoid cells (Plate II, Figures 1, 2, 3; Plate III, Figure 1). 

 The majority of the lymphocytomas (118 cases) were of this type. In 51 cases 



