14 MASS. EXPERIMENT STATION BULLETIN 391 



and nodular form of the disease. Practically no difference was noted in the 

 various grades of involvement between the group of lymphocytomas in which 

 nerve tissue was affected and the group in which the nerves were free of tumor. 



The organs of some of the cases of lymphocytoma w'ere weighed at the time 

 of necropsy. The weights of the organs most commonly found affected with 

 lymphocytoma are listed in Table 9. They are expressed as percentage of carcass 

 weight so that comparisons ma\- be made between the different groups. No 

 attempt was made to distinguish between the weight of organs with different 

 degrees of involvement, although those with Grade 4 infiltration were usually 

 heavier than those with less infiltration. The relative number of different grades 

 included in the various groups is approximately comparable. In a few instances 

 weights were obtained on unaffected organs of birds with lymphocytoma. These 

 are indicated in Table 9 and serve for comparison with weights of affected organs. 

 The standard error of the mean was calculated for each group. The mean values 

 for the liver, kidney, and ovary when affected with diffuse lymphocytoma were 

 larger than when they were affected with either of the ether two forms of lym- 

 phocytoma. In the case of the spleen, the differences were not significant. A 

 comparison of the group with nerves affected and the group with nerves not 

 affected indicates a smaller liver and spleen and a larger kidney and ovary in 

 cases in which the nerves were also involved, but only in the case of the liver was 

 the difference statistically significant. 



Egg Production. — Data on the egg production of chickens that developed 

 lymphocytoma were available for only 15 cases (Table 10). These data are 

 meager yet they suggest certain features on which more information is needed. 

 All of these cases came from one flock on which careful records were kept. The 

 productive life, that is, the interval between the first and last egg produced, 

 varied from 3 to 333 days (average, 104' days). During this time the birds laid 

 from 2 to 176 eggs (average, 60 eggs). The productive index as used is an arbi- 

 trary value obtained by dividing the number of eggs laid by the productive life 

 in days. This factor varied from 0.074 to 0.863 and averaged 0.584. A similar 

 production index was calculated from the records of the flock in which these 

 cases were found. Inasmuch as the average productive life of the diseased birds 

 was the first 108 da>s of production, a comparable set of figures was obtained 

 from the flock records. The production of the flock during the first 150 days 

 of the laying period averaged 80 eggs per hen, which provides a production index 

 of 0.534 that may be compared with the findings in the cases of lymphocytoma. 

 Ten of the hens with Ij-mphocytoma had laid 25 or more eggs before developing 

 the disease; and of these, eight had a production index higher and two a produc- 

 tion index lower than the average for the flock. These results, compared with the 

 slightly higher average production index for the group that developed lympho- 

 cytoma suggest that those hens which developed the disease were average to good 

 producers. 



Another point of interest in connection with egg production was the interval 

 between cessation of egg laying and necropsy. It seems obvious that the presence 

 of a disease condition such as lymphocytoma would have an effect on egg pro- 

 duction. It is generally recognized that many acute diseases of chickens, such as 

 respiratory infections, will cause a sudden decrease or cessation of egg production. 

 The interval between the last egg laid and necropsy of a case of lymphocytoma 

 may give some indication of the duration of the disease. In the cases reported, 

 this period was relatively short, averaging 38 days and ranging from 4 to 73 days 

 (in eight of the cases the interval was from 30 to 40 days). The extremely short 

 interval of 4 days noted in Case T 1743 may have been due to the fact that the 

 tumc of the bursa of Fabricius caused sufficient obstruction to preclude laying 



