CIRCULATING, SYSTEM. 359 
while aerated blood was 1.0300. 'This circumstance was con- 
sidered as furnishing a strong support to a theory of animal 
heat, long in vogue, and which we shall notice afterwards. 
Dr Joun Davy, however, in the course of his experiments, 
obtained results which differed from the foregoing. He 
found the specific heat of venous blood to be 0.903, while 
that of aerated blood was 0.913. Both these results indicate 
a diminution in the specific heat to have taken place. It may 
be proper, however, to state, that it is very difficult, if not 
impracticable, to obtain accurate results in such attempts. 
Whether the blood is poured into an equal bulk of ano 
ther fluid, whose specific heat is known, for the purpose of 
_ascertaining the resulting temperature of the mixture, or 
its rate of cooling be employed, there are changes which 
begin to take place in its constitution from the moment it 
_leaves the bloodvessels, which must affect the accuracy of 
the comparison. The experiments of Darwrn, already 
quoted, prove; that the blood is altered im the course of 
flowing through the air from the veins into the cup in 
which it is received. 
The quantity of oxygen consumed by animals in a given 
time, is variable, not only in regard to species and indivi- 
duals, but in the same individuals in different circumstan- 
ces. In man, the quantity of oxygen consumed in a minute, 
has been differently rated by chemists. ALLEN and Pepys 
found it to be 26.6 cubic inches in a minute; Davy 31.6, 
and Murray 36. The quantity, however, is found to 
vary under the following states of the system. 
Muscular exertion appears to increase the consumption 
of oxygen, according to Securn, nearly fourfold beyond 
the usual quantity. Dr Prour*, who has examined this 
* Annals of Phil, ii. p. 328—343, and iv. p. 331—337. 
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