ON INCREMENT OF ANIMAL HEAT. 419 
by certain external signs, which, from stage to stage, steadily 
indicate its degree. 
Fatal Increment of Animal Heat. 
The increment of heat in a warm-blooded animal which 
proves fatal is from 11 to 12 degrees on Fahrenheit’s scale. 
I have never seen a recovery under any after condition when 
once the increment of 12 degrees has been reached, and I 
seen a fatal result from 10 and 11 degrees. The rule seems 
to be subject to so few variations it may be accepted as prac¬ 
tically absolute. In animals having naturally a difference of 
temperature the rule holds equally good. Thus a pigeon 
having a natural mean temperature of 108° will succumb 
w'hen the temperature of its body is raised to 120°, and a 
pigeon having a natural mean temperature of 106° will suc¬ 
cumb when its temperature is raised to 118°. A rabbit 
having a temperature of 104° will succumb when its tempera¬ 
ture is raised to ll6°, and a cat having a temperature of 102° 
will succumb when its temperature is raised to 114°. In 
brief, the 12 degrees of heat on Fahrenheit’s scale added to 
the natural degree of heat of the animal becomes the fatal 
degree. I believe the same rule applies to man. 
In order to determine the fact I have named, an amount of 
labour and care has been required which at first sight might 
seem improbable. Judge for yourselves how far possible 
sources of error have been excluded, and pray, if you see a 
fallacious step, tell me of it. We use for our research an 
inner chamber of glass. The chamber is water-tight; it has 
a movable floor covered with thick felt. It is placed in 
an outer chamber coated with felt. It is fed steadily with 
air warmed by passing through a metallic coil, and so 
accurately does the current of air carry its charge of heat, 
that for any number of hours the variation of one degree is 
not observed. The air is, moreover, undergoing the most 
perfect change, so that the accumulation of carbonic acid is 
not possible. We place the subject for observation in the 
inner chamber, surrounding it, gently, with some non-con¬ 
ducting woollen substance, or a soft pillow, and it is unne¬ 
cessary under such circumstances to make the air in any 
degree painfully warm or difficult to breathe ; for when the 
conditions for radiation from the body, and for the loss of 
force by motion, are cut off, the accumulation of heat is quick 
enough, without any forcing of the process against time. 
XLII. 
30 
