1911-12.] Effects of Seasonal Changes on Body Temperature. 113 
suppose that there may exist in the animal body phases — diurnal, lunar, 
or seasonal — in which the body temperature undergoes cyclical or periodic 
variations comparable with the changes that take place during the oestrous 
cycle in the mature female, or in the mental functions of the insane in the 
condition known as folie circulaire. In this relation it is important to 
make a detailed study of the body temperature in association with the 
seasonal or other changes of habit which all animals exhibit to a greater 
or less degree. 
Amongst homoiothermal animals no class gives greater evidence of 
cyclical changes than do birds ; in the late summer and autumn they show 
distinct signs of depressed vitality, such as casting of the feathers and (in 
the case of the domesticated fowls) a falling off* in egg-production, while 
in the early spring they change plumage in preparation for the mating and 
breeding season, and in other respects give evidence of increased activity. 
No systematic investigation, so far as I know, has been made on the body 
temperature of birds from this point of view. 
In the present investigation it was at first intended to make one series 
of observations in the spring of the year, and another in the autumn, and 
to use wild birds for the purpose, since it seemed probable that seasonal 
changes would be more firmly established in these than in domestic species. 
Various circumstances arose, however, which prevented the original plan 
from being carried out, and although a large number of figures were 
collected, they could not be divided into spring and autumn groups for each 
species. These results have already been presented to this Society and 
published in its Proceedings.* 
It was then resolved to make an extended and detailed study of body 
temperature in the domestic fowl, not only in the spring and autumn 
months, but throughout the whole year, and the opportunity of doing this 
presented itself when the writer, through the kindness of Professor Rice, 
obtained access to the extensive colony of hens in the Department of Poultry 
Husbandry at the New York State College of Agriculture. It is essential 
in comparative work of this kind that the conditions shall be the same 
throughout the year except in so far as these are influenced by the weather, 
and that the observations be made periodically on the same individuals, 
and at the same hour of the day, and for the purpose in view the arrange- 
ments in the Poultry Department were all that could be desired. 
The birds were lodged in commodious wooden hen-houses of the most 
recent type ; the upper half of the front wall which faced the south being 
closed in by wire-netting only, and through a small window in the back 
* Simpson, Proc. Roy. Soc. Edin., 1911-1912. 
VOL. XXXII. 
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