418 
ON INCREMENT OF ANIMAL HEAT. 
seems, on mere statement, incredible. But animals such as 
the fowl, the pigeon, and the cat, whose bodies, surrounded 
by good non-conducting material, eliminate water slowly, are 
very differently constituted, and are charged with a fatal in¬ 
crement of heat with comparative readiness. For example, I 
myself entered a hot-air bath the temperature of which 
reached 212® Fahr. In this air the albumen of an egg co¬ 
agulated in ten minutes. I had, however, no difficulty in 
living under this condition for twenty minutes, and I came 
out of the ordeal uninjured ; but a fowl in the chamber with 
me, breathing the same air, was struck instantly by the heat, 
in three minutes was insensible, gasping, tetanic; and, taken 
out at once into air at 65° F., was unable to recover. At 
what temperature a man would die from exposure to heated 
air is not as yet known ; but respecting the lower animals 
the facts are within reach. In the case of the pigeon, the 
duck, the common fowl, the cat, the guinea-pig, and the 
rabbit, the temperature of 145° to 150° Fahr., is sufficient to 
lead to fatal increment of animal temperature. Great varia¬ 
tions nevertheless may be observed in the opposition to in¬ 
crement of heat offered even by these animals. If the animals 
be allowed free motion of body, there is resolution of heat 
into motion, and therewith a capacity for living action, which 
may be wonderfully pronounced. In fact, experimental ob¬ 
servation based on the temperature of the air only would be 
fallacious and useless. 
To arrive, therefore, at exact facts respecting the increment 
of heat in animals, we must let the observation of surrounding 
temperature hold a secondary place. If we take care to impede 
the radiation of heat from the body of an animAl, we may 
produce fatal effects even from summer heat. If we do not 
take this precaution, we must increase the temperature. 
Under either condition we shall do no injury until the body 
of the animal itself is elevated in temperature up to a given 
degree ; in other words, whatever may be the outer tempera¬ 
ture, a certain increment of heat within the body itself must 
be reached before there is danger. 
Can this fatal increment of heat be determined with any 
degree of exactitude ? Is it variable or steady in different 
animals ? Is it marked, in intensity, by outward symptoms 
or signs ? 
To these questions—which, indeed, are first principles in 
the physical reading of disease—I give an affirmative answer. 
The fatal increment of animal heat is readily determined ; in 
warm-blooded animals it is more variable than the natural 
variations of ordinary animal temperature, and it is marked 
