NEOPLASTIC DISEASES IN CHICKENS 7 



for examination was 32.8 weeks, and most of these were moribund. Birds 

 with lymphocytoma involving nerves were significantly younger when killed 

 (Table 3). This is no doubt due to the fact that birds with nerve involvement 

 showed symptoms (caused by the nerve lesions) earlier than birds with no nerve 

 involvement, and the chickens were submitted for examination because of the 

 symptoms. There was no significant difference between the six groups in age 

 of birds that died (Table 3). 



Table 3. — Age of Birds at Necropsy in 213 Cases of Lymphocytoma. 



Age is expressed in weeks with standard error of the mean. Figures in parentheses 

 are number of cases in group. 



Sex. — The effect which the factor of sex ma\- have on lymphoc\'toma is some- 

 what difficult to determine from the data. There were 193 females and 20 males 

 represented in the 213 cases, which is a ratio of 9.7 to 1. A similar ratio of 9.7 

 to 1 existed in the 118 cases of diffuse lymphocytoma; but the ratio dropped to 

 4 to 1 in the 20 cases of nodular lymphoc\toma and increased to 14 to 1 in the 

 75 cases of combined diffuse and nodular lymphocytoma. There was a slight 

 and perhaps insignificant difference in the sex ratios of the cases of lymphocytoma 

 with nerve infiltration and those without involvement of nerves. The ratios 

 were 12.8 to 1 (83 cases) and 8.3 to 1 (130 cases), respectively. These results 

 suggest that a male is more apt to have the nodular form of the disease than a 

 female and that a female is more apt to have the diffuse and nodular form of the 

 disease than a male. The incidence of lymphocytoma in male and female chickens 

 is covered miore fulh under incidence in sexes in the general discussion. 



Seasonal Occurrence. — More cases of lymphocytoma were encountered during 

 the first and last quarters of the year than during the second and third quarters 

 (Table 4). Such frequency of incidence during these periods must be correlated 

 with the ages of the birds aS the majority of chickens in commercial poultry 

 plants would be about 35 weeks old during the first and fourth quarters of a 

 year. This subject is covered in more detail in the discussion on incidence of 

 neoplasia. An interesting feature was the shift of high incidence of lympho- 

 cytoma in which nerves were involved from the fourth to the third quarter. This 

 fact must also be correlated with the observation that such cases occurred in 

 birds slightly younger than those in which no nerves are affected. When all 83 

 cases of lymphoc\toma with involvement of nerves are considered, there were 

 two peaks of high incidence, these being in the first and third quarters of the year. 

 This finding has not been explained. The various types of lymphocytoma (diffuse, 

 nodular, and diffuse and nodular) were essentially similar with respect to their 

 incidence in the different quarters of the year. 



