398 



Journal of Agricultural Research 



Vol. V. No. 9 



either died from or were killed because of disease, and, second, in appar- 

 ently normal birds accidentally killed or killed for data. 



Table I. — Percentage of tumors found in birds dead from natural causes and in normal 

 birds which were killed 



This table shows that there was no significant difference in percent- 

 age of tumors found between the two groups of birds. Some of the 

 tumors found in the apparently normal birds were probably early stages 

 of tumors which might later have caused the death of the individual 

 affected. A study of the individual cases of birds with tumors (see 

 Table IV) shows that while in several cases the tumors were the prob- 

 able cause of death, yet there were many others among the birds which 

 died from natural causes in which the cause of death was entirely 

 unrelated to the presence of the tumor. The close agreement of the 

 two groups in percentage of birds with tumors strengthens the con- 

 clusion that in this flock at least there are about 90 cases of tumors per 

 1 ,000 birds. 



In order to study the influence of age and sex upon the occurrence 

 of tumors, age-frequency distributions were made for each sex. The 

 birds were grouped into half-year classes. There were a few birds whose 

 exact age was not known. These could be classified as "young" (under 

 2 years) or "old" (over 2 years). The percentage of the birds of each 

 age group which had tumors was then calculated separately for each sex 

 and for the two sexes together. These data are given in Table II. 



This table shows that of the 880 birds only 44 were males, while 836 

 were females. This difference is due merely to the fact that in the adult 

 flocks only a few males were kept (for breeding purposes) and a great 

 many females. It indicates nothing as to the relative morbidity of 

 males and females. Considering the small number of males, it is pos- 

 sible that the apparent difference in the sexes in regard to the occurrence 

 of tumors, 6.82 per cent in the males and 9.09 per cent in the females, 

 may not be significant. A study of the individual cases, however (see 

 Table IV), shows that the organs most frequently affected in the females 

 are the genital organs. It may easily be that on this account there is 

 a real difference in the sexes. 



A study of Table II shows that there is a significant correlation between 

 age and the percentage of birds which have tumors. This is also shown 

 in Table III, which is a summary of the data in Table II, combining the 



