1911-12.] Effects of Seasonal Changes on Body Temperature. 135 
temperature, and the smallest and most active birds the highest. Compare 
in this relation the Barred Plymouth Rocks with the Brown Leghorns. 
Summary. 
Monthly observations, extending over one year, were made on the rectal 
temperature of 114 domestic fowls (Gallus gallus, $) and records from forty- 
one of these were obtained for two years. Six different breeds were used, 
each located in a separate pen, all under similar conditions, and the 
mean temperatures for each group were plotted out to form an annual 
temperature curve. It was found that — 
1. The lowest temperatures occur in December, January, and February, 
and the highest in June, July, and August, corresponding in a general way 
with the temperature of the external air. 
2. Barometric pressure does not appear to have any influence on the 
body temperature of the hen. 
3. The curve of egg-production does not coincide with the annual 
temperature curve, the former reaching its highest level in April and May, 
the latter in June, July, and August. 
If we compare the mean rectal temperature at two periods of the year 
when the external or weather conditions are approximately the same (April 
-May and September-October), but when the vitality of the birds, as 
indicated by the curve of egg-production, moulting, etc., is at a maximum 
and minimum respectively, we find that the figures are practically identical. 
This would seem to show that cyclical bodily changes have little effect on 
body temperature as compared with outside influences. 
In conclusion I should like to express my sense of indebtedness to 
Professor Rice for granting me permission to carry on the work in his 
department, and to Mr W. G. Ivrum for assistance while it was in progress. 
{Issued separately April 29, 1912.) 
