CIRCULATING SYSTEM. 



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 JOHN 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 DARWIN, already 

 quoted, prove, that the blood is altered in 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 SEGUIN, nearly fourfold beyond 

 the usual quantity. Dr PROUT *, who has examined this- 



* Annals of Phil. ii. p. 328343, and iv. p. 331 337. 



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