COMBUSTION IN THE BODY. 343 



that this cannot occur out of the body without 

 the extrication of heat ; therefore the union of 

 blood-materials in the lungs with oxygen must 

 produce heat. Again, in the minute vessels, 

 called capillaries, which exist in almost every 

 portion of the frame, oxidation takes place, for 

 the arterial blood gives oxygen to the tissues, 

 among which it circulates ; here again, there- 

 fore, heat must be eliminated. Thus we see 

 that the body possesses two sources, or rather 

 two localities for the evolution of heat the 

 lungs and the capillaries ; in other words, heat 

 is evolved all over the frame, and particularly 

 in the lungs. The perpetual ingress of cold air? 

 and the enormous loss of heat by evaporation, 

 demand that the lungs should be specially pro- 

 vided for; and this is considered to be effected 

 by the perpetual oxidation taking place there. 

 While, however, this is true to some extent, 

 there can be little doubt that the animal frame 

 possesses other sources of heat in addition to 

 that of respiration derived from the process of 

 oxidation. 



The carbonic acid given out in respiration 

 is a sufficient proof that carbon has been burnt 

 somewhere, for when carbon burns in air it 

 forms carbonic acid gas, and the above consi- 

 deration indicates the locality where this heat- 

 producing process takes place. Respiration is 

 really and truly a process of combustion. The 



