1911— 12. J Effects of Seasonal Changes on Body Temperature. 131 
When we compare the body temperatures on dates about equal distances 
on the two sides of the hot summer weather, when all the external 
conditions are approximately the same, e.g. April with October, and May 
with September, we find that there is practically no difference. The mean 
for all the birds (114) of which the records were kept for one year was as 
follows : — April 4T86° F., October 4F90°, May 4P93 0 , September 41’99°. It 
would appear, therefore, that a high external temperature has a distinct 
influence on the body temperature of the hen, and that this is the main 
factor in raising it in the hot weather which usually prevails in the State 
of New York in June/July, and August. It must be kept in mind that 
this applies only to the hours when the observations were made, viz. from 
1.30 to 4.30 p.m. when the temperature of all homoiothermal animals 
attains its maximum. Whether the mean temperature for the twenty-four 
hour period is affected in the same sense we are unable to say. It is not so 
clear that the fall in body temperature in the winter months is due to the 
cold weather experienced in December, January, and February, since other 
factors (lack of opportunity for much muscular exercise, and diminished 
sunlight) are in operation at the same time. 
In the hen the body temperature does not appear to be affected in any 
way by the barometric pressure, although it has been stated that a relation- 
ship does exist between the two in the human subject. It is difficult to 
understand, however, how this can be. 
A weather condition more likely to influence body temperature would 
be humidity, but for this it has not been possible to plot a curve, since the 
daily records were taken at 8 a.m., and from this it could not be estimated 
with any degree of accuracy what the humidity would be in the afternoon 
at the hours when the temperature observations were made. 
When the curves obtained from the reduced number of hens from which 
records were collected over two years are examined, it will be found that 
the second year agrees with the first fairly closely, until we come to the 
summer months, and here the curve of mean temperature is very irregular 
and does not rise as it did the former summer, although the external tempera- 
ture is practically the same. The chief reason for this irregularity and the 
apparently low temperature is to be found in the fact that in the second 
summer, when the birds were two years old, a large proportion of them 
happened to be broody on the days when the temperatures were being 
taken, and in this condition, as is well known, the body temperature is 
always low. This reduced the mean for the whole. For example, in Pen 
VI. (Rhode Island Reds), on June 21, 1911, two out of seven were found 
sitting in a corner of the room on one or two eggs ;• these had temperatures 
