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 
Manner of death. 
Total num¬ 
ber of birds. 
Percentage 
of birds 
with tumors 
present. 
Natural causes. 
660 
220 
8.94 
9.09 
Killed. 
Total. 
880 
8. 98 
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 
