ON INCREMENT OF ANIMAL HEAT. 
415 
range itself. I have one pigeon, for instance, which has a 
natural range of temperature running from 107° to 111° F., 
the mean being 109°. I have another pigeon in which the 
natural range is from 105° to 107°, the mean 106° F. 
4. In considering the temperature of the animal body in 
different individuals of the same species, age must be carefully 
taken into account. I believe it will be found in the course 
of further experimental inquiry that each period of life is 
marked by a distinct thermal range, and that what would be 
a natural thermal reading at one period of life would be un¬ 
natural at another. In the case of the two pigeons noticed 
'above, age is probably the cause of the difference, for the bird 
with the lower temperature is three years older than its neigh¬ 
bour with the higher temperature. Metcalfe, who made a 
series of observations as to the temperature of kids and goats, 
cats and kittens, and young and old horses, drew a similar 
inference. Thus in a she-goat three months old, he found 
the temperature of the body was 107°, while in the mother of 
the same animal the temperature was 104°. In a kitten two 
months old the temperature was 105'5°; in a vigorous, nearly 
full-grown cat, 104°; in a full-grown cat three years old, and 
mother of the kitten, 103’5°; and in a cat in the nineteenth 
year, 102°. In a horse four years old, he found a tempera¬ 
ture of 104°, and in a mare twenty years old 100° F. In the 
human subject, a sufficient number of observations have not 
been conducted to enable one to speak with precision on the 
ranges of temperature according to age; but the general fact 
that there is variation, and that there is persistent decrease 
in the advanced periods of life, is proved. It will take some 
years of careful and patient research to observe and write 
down the all-important details bearing on this subject. It is 
clear that in the aged there is not merely an objective decrease 
of heat—that is to say, not a mere decrease of sensible heat— 
but a decrement also of specific heat, so that the body in 
advanced life is less able to oppose great fluctuations of 
atmospheric temperature. 
5. Iffie condition of the body in respect to fatness or lean¬ 
ness is another modifying influence to be remembered in 
estimating animal temperature. As a rule, a body in good 
condition has a higher standard of temperature than a body 
that is badly nourished, or than a body that is unduly loaded 
with fat, and one very important observation deserves to be 
made in relation to the presence of fat in young and active 
bodies. The observation is this—that whenever in such sub¬ 
ject there is within the organism a cause at work leading to 
an undue accumulation of heat, there is, owing to the imper- 
