562 
ON ANIMAL HEAT. 
keeps itself much cooler than the surrounding atmosphere. Dr. 
Davy found that the internal temperature of the human body, 
when exposed to a tropical climate, was from 2.7° to 3.6° Fahr. 
higher than in the more temperate climates. The French natu- 
ralists appointed to the Bonite also investigated this subject. 
They made numerous experiments, and the inference from them 
was, that the heat of the human body rises and falls, in a slight 
degree only, with that of the external temperature ; and that it 
falls slowly in passing from a hot to a cold climate, but rises 
rather more rapidly in returning towards the torrid zone. 
24. Experiments have been instituted in order to ascertain 
the effect of high artificial heat on the animal economy. Blag- 
den, Fordyce, Banks, and others, have exposed themselves to 
heated apartments, varying between 198° and 2il° Fahr., and 
for a short time even so high as 260°. But they found that the 
body possessed capabilities of maintaining nearly its original 
temperature from the cooling effect of increased perspiration. 
That it was due to this circumstance was substantiated by De la 
Roche, who, having heated the atmosphere of an apartment, and 
at the same time saturated it with moisture, in order to prevent 
exhalation from the skin, found that the heat of the body when 
so exposed rose from 4° to 9° Fahr. 
25. Having briefly directed attention to the principal facts 
that have been already ascertained to accompany the exercise 
of this important function, it now remains to point to those 
means by which it is supposed vital heat is generated and sup- 
ported within the body. Among the most popular and plausible 
of modern theories on the subject is the one propagated by the 
joint exertions of Lavoisier and Laplace. Knowing that heat 
often resulted from chemical changes in inorganic matter, they 
ingeniously supposed that something similar occurred during the 
performance of the respiratory process, an animal function par- 
taking of a chemical character. In this act the oxygen of the 
atmosphere combines with the carbon of the blood in the lungs 
and forms carbonic acid, which is thrown off during expiration. 
But by carefully measuring the quantity of carbonic acid so 
formed, and the quantity of oxygen lost, it has been ascertained 
that more oxygen disappears than is necessary to the formation 
of the carbonic acid. To meet this slight discrepancy it has been 
supposed that this portion of oxygen, which does not participate 
in the combination with the carbon, unites with the hydrogen in 
the blood, and forms water, which is exhaled. The theory of 
those who maintain respiration to be the main source of animal 
heat, is founded on the hypothesis that during these combina- 
tions a quantity of heat is evolved, which is immediately ab- 
