46 



MASS. EXPERIMENT STATION BULLETIN 391 



results tend to indicate a relatively high incidence ot lymphocytoma in cross- 

 bred birds, the majority of which were the progeny from mating Rhode Island 

 Reds with Barred Plymouth Rocks (Table 23). Several factors would influence 

 this result ; for example, the age group of birds examined and the number of flocks 

 and breeding strains represented would be of significance. When the com- 

 parison between breeds was drawn and the frequency of incidence of lympho- 

 cytoma was based upon the cases found in the age group of from 7 to 12 months, 

 the figures obtained were 9.9 percent for Rhode Island Red, 10.4 percent for 

 Barred Plymouth Rock, and 13.6 percent for crossbred chickens. The difference 

 was still apparent, and became more significant when the source of material was 

 considered. The 103 cases of lymphocytoma in Rhode Island Red chickens 

 came from not more than 48 sources (flocks or breeding strains) or an average of 

 2.14 cases per source. The 22 cases of hmphocytoma in crossbred birds were 

 obtained from not more than 10 sources averaging 2.2 cases per source. The 

 14 cases in Barred Plymouth Rock chickens came from not more than 8 sources 

 or an average of approximately 1.7 birds per source. Since the cases in Barred 

 Plymouth Rock birds came from relatively fewer sources, it seems that the figure 

 for incidence in the breed may be slightly too high. The result at least indicates 

 need of more data. 



T.\BLE 23. — Incidence of Neoplasia with Respect to Breed. 

 Data from Collections A and B. 



♦Includes all those listed in Table 22. 



The results for myelocytoma, fibrosarcoma, and leukosis, indicating a lower 

 relative incidence in Rhode Island Red chickens, are based on too few examples 

 to be regarded as definitely significant. 



Age at Necropsy 



The averages together with the low and high values for age at necropsy of 

 chickens affected with the various tumors are listed in Table 22. It may be 

 noted that certain tumors were more apt to be found in birds of a given age group 

 than others. For example, lymphocytoma, embryonal nephroma, and myelo- 

 cytoma appear to have been more common in birds 8 to 10 months of age; fibro- 

 sarcoma in a slightly older age group; and leukosis in birds about one year of 

 age. Leiomyoma, epithelioblastoma, and carcinosarcoma were characterized 

 by their occurrence in older birds. 



Mathews (17) stated that the myelocytoma cases studied by him were found 

 principally in birds less than one year of age; whereas Ij'mphocytoma was found 

 in birds of all ages. The present data support his claim, for the oldest bird in 

 which myelocytoma was found was aged 56 weeks. The average of one year for 

 the age of 12 birds with spontaneous leukosis found by Feldman and Olson (8) is 



