40 Mr. Brodie’s Experiments on the 
strong and frequent : but at the end of one hour and forty 
minutes the pulse had fallen to 24 in a minute. 
The blood in the arteries was seen of a florid red, and that 
in the veins of a dark colour. 
A small opening was made in the abdominal muscles, 
through which the thermometer was introduced into the 
abdomen, and allowed to remain among the viscera. 
At the end of an hour the heat in the abdomen had fallen 
from ioo° to 89°. At the end of an hour and forty minutes in 
the same situation the heat had fallen to 85°, and when the 
bulb of the thermometer was placed in the thorax in contact 
with the lungs the mercury fell to 82°. 
It has been a very generally received opinion that the heat 
of warm-blooded animals is dependant on the chemical changes 
produced on the blood by the air in respiration. In the two last 
experiments the animals cooled very rapidly, notwithstanding 
the blood appeared to undergo the usual changes in the lungs, 
and I was therefore induced to doubt whether the above men- 
tioned opinion respecting the source of animal heat is correct 
No positive conclusions however could be deduced from these 
experiments. If animal heat depends on the changes pro- 
duced on the blood by the air in respiration, its being kept 
up to the natural standard, or otherwise, must depend on the 
quantity of air inspired, and on the quantity of blood passing 
through the lungs in a given space of time : in other words, 
it must be in proportion to the fullness and frequency of the 
pulse, and the fullness and frequency of the inspirations. It 
therefore became necessary to pay particular attention to these 
circumstances. 
