VI. 
Animal Temperature. 
HE higher animals have within their bodies some source of heat 
and some mechanism to regulate the production and loss of that 
heat, for, equally in the height of summer as in the depth of winter, 
their mean temperature is constant. This fact was known to the 
Ancients, but imperfectly; they had no thermometers, no exact 
methods of determining temperature. They judged from their 
sensations, but here sensations are imperfect guides. 
A patient attacked by an ague feels chilly, miserably cold; he 
huddles up by a fire, he shivers, and his teeth chatter ; he says that 
he is cold, but at this precise moment he is in a fever-heat. How 
does this contradiction arise? The feeling of heat or cold arises in 
the nervous structures of the skin. When these nerve-endings are 
flushed by a rapid stream of blood, there is a sensation of warmth ; 
should the blood supply be small, not enough to compensate for the 
loss of heat by radiation and conduction, there arises a sensation of 
cold. During the vigor, for such is the name given to the early stage 
of ague, the vessels of the skin are contracted, the skin is pale and 
cold, its temperature twelve or sixteen degrees below the normal blood- 
heat; but, at the same time, the temperature of the internal parts has 
risen six or seven degrees above the normal. 
Let the converse condition be studied in the same disease during 
its third or sweating stage. The skin is now red and flushed, its 
blood-vessels are dilated; the patient is bathed in perspiration; he 
says that he is intensely hot, although his internal temperature is 
rapidly falling to the normal. 
Animal heat the Ancients considered to be beyond the reach of 
physical or chemical laws. They could assign no cause for it, and 
therefore looked upon it as some innate quality, something essentially 
‘“‘ vital.” This * vital” heat was supposed to be concentrated in the 
heart, and to be distributed to the body by the blood in the veins; it 
was prevented from accumulating by respiration, the chief function of 
which was to cool or temper the blood. 
After the year 1595 it was first possible to determine the tempera- 
ture of the body more exactly, and to make observations upon the 
independence of the temperature on external conditions. It was 
about this time that Galileo invented the thermometer. As observa- 
