11(5 OF ANIMAL HEAT. 



he says, to the succession of cool air sent into the lungs. He 

 therefore concludes, that animal heat depends much more upon 

 the nervous energy than ujxjn die chemical changes of the 

 blood. But Le Gallois asserts, that under artificial respiration 

 the temperature falls, even if every part remain uninjured.* 

 Dr. Crawford himself states that the chemical process of respi- 

 ration may, in certain cases, be the means of cooling the body. 

 If the pulmonary exhalation is in very great abundance, it will 

 carry off so much of the heat given out during the change of the 

 oxygen into carbonic acid, that there may not be sufficient to 

 saturate the increased capacity of the arterial blood ; this fc ill 

 therefore absorb heat from the system, as it passes along, till its 

 temperature equals that of the other parts, f 



Many circumstances, however, favour the doctrine of Crawford. 

 In high temperatures we have less necessity for the evolution of 

 heat by the chemical changes of the blood and air, whereas, in 

 low temperatures, as more heat is required to sustain the natural 

 degree of temperature, the chemical changes are more necessary. 

 Accordingly, in very high temperatures, the arterial blood 

 remains arterial, — is as florid in the veins as in the arteries, and 

 the inspired air is less vitiated ; in low temjieratures, the venous 

 blood is extremely dark, and the inspired air more vitiated. J 



The temperature is also regulated by the degree of perspi- 

 ration, the momentum of the blood, &c. In proportion as more 

 vapour transpires from the skin, will more heat be carried off, 

 whence M. Delaroche heated animals at pleasure like inanimate 

 matter by saturating their atmosphere with humidity, thus pre- 

 venting cutaneous and pulmonary evaporation. And as the sum 

 of the tmantity and velocity of blood in any jmrt is greater, the 

 temperature of that part will be higher. Whether •Crawford's 

 theory be correct or not, the production of animal temperature 

 must still be as evidently a chemical process as changes of tem- 

 perature among inanimate bodies. Jhit tliis does not prevent it 



• Sir le Principe de la vie. f \. c , p . 388. 



X Crawford oh Animal Heat. p. 387 aq. 



