NEOPLASTIC DISEASES IX CHICKENS 17 



invaded the nerve from without, for the nerve was the more lightly infiltrated 

 (Plate III, Figure 2). In 3 cases, lymphocytoma was confined to the soft tissue 

 surrounding nerves in the regions of either the brachial or lumbosacral plexuses 

 and immediate radicals. 



An interesting finding in this collection of lymphocytomas was the relatively 

 small number of cases of the nodular type in which nerves were involved (Table 2). 

 A ratio of about 2 to 3 existed between the cases with and without nerve involve- 

 ment when lymphocytoma was either diffuse or diffuse and nodular in type. 

 This ratio changed to 1 to 9 in nodular lymphocytoma. Actually only two cases 

 of nodular lymphocytoma were observed in which nerves were involved. One 

 of these was an extension of lymphocytoma of the adrenal and ovary into an 

 anterior mesenteric nerve ganglion and might easily have been overlooked. 

 The significance of this finding is obscure. The number of cases is small, and it is 

 possible that the observation may be due to chance. 



The explanation of the group of 60 cases with nerve involvement at a site re- 

 moved from lymphocytoma of other tissue is subject to a difference of opinion. 

 A number of conceptions are possible. They may represent instances of metas- 

 tasis of the tumor to a nerve from a primary focus situated in a visceral organ. 

 They maN' have developed in the nerve in response to a hypothetical causative 

 agent of lymphocytoma. They may be lesions of fowl paralysis existing ccinci- 

 dentally with lymphocytoma, assuming that there are separate agents respon- 

 sible for each disease. Or a single agent may be responsible for both lymphocytoma 

 and fowl paralysis and the response in nerve or other tissue depend upon factors 

 as yet unknown. These questions cannot be answered from the data, and a satis- 

 factory explanation must await settlement of the problem of etiology of the 

 diseases. 



No satisfactory explanation has been advanced for the existence of different 

 types of lymphocytoma. Nodular and diffuse lymphocytoma have been rec- 

 ognized and described by Feldman (7) and Mathews and Walkey (19), as well 

 as others; and another manifestation — combined diffuse and nodular lympho- 

 cytoma — has appeared in this study. A possible explanation for these different 

 types has developed as a result of this study, based on the theory that the host 

 exerts a variable degree of resistance against growth of the tumor. Thus, diffuse 

 lymphocytoma is a disease in which little resistance is offered on the part of 

 the host, and the nodular form develops when considerable resistance to growth 

 is offered. The diffuse and nodular form results when the resistance is moderate 

 in degree. The data do not provide conclusive evidence for such a theory, but 

 do offer some support. On the basis of such a contention, one would expect that 

 the type of disease in which most resistance was offered by the host would be 

 the least widespread, and this was the finding in the case of nodular lympho- 

 cytoma (Table 6). One might also expect that the degree of individual organ 

 involvement would be least in the nodular form, and it was found that 37.9 

 percent of the affected organs were Grade 1 or 2 in cases of nodular lympho- 

 cytoma as compared to 29.4 percent Grade 1 or 2 in cases of diffuse lymphocytoma 

 (Table 8). Although data with respect to organ weights indicated no statistically 

 significant difference between the three forms of lymphocytoma (except in the 

 case of the kidney), the suggestion remains that the relative weights are greater 

 in diffuse lymphoc\toma. A larger series of cases in which the organs have com- 

 parable grades of involvement should be examined to settle this point. The 

 histology of the different types also lends itself to support of the theory of re- 

 sistance on the part of the host. A nodular, circumscribed focus of lympho- 

 cytoma surrounded by a connective tissue wall of variable thickness suggests an 

 attempt on the part of the host to localize and wall off the tumor from the rest 

 of the body (Plate III, Figure 4). Reactions of this type have been noted in 



