ANIMAL HEAT. O95 



refer to any known causes, we are perfectly unable to 

 imagine the sources from which they spring. 



It will be interesting now to examine the phenomena 

 of animal heat, the consideration of which naturally leads 

 us to consider the digestive system, the circulatory pro- 

 cesses, and the effects of nervous excitation. 



The theory, which attributes animal heat to the 

 combination of the carbon of the food taken into the 

 stomach with the oxygen of the air inspired through 

 the lungs, has become a very favourite one. It must, 

 however, be remembered that it is by no means new. 

 The doctrines of Brown, known as the Brunonian 

 system, and set forth in his Elementa Medicines^ are 

 founded upon similar hasty generalizations. Although, 

 without doubt, true in a certain degree, it is not so to 

 the extent to w r hich its advocates would have us believe. 

 That the carbonaceous matter received into the stomach, 

 after having undergone the process of digestion, enters 

 into combination with the oxygen breathed through the 

 lungs or absorbed by the skin, and is given off from 

 the body in the form of carbonic acid, and that, during the 

 combination, heat is produced, by a process similar to 

 that of ordinary combustion, is an established fact ; but 

 the idea of referring animal heat entirely to this chemical 

 source, when there are other well-known causes pro- 

 ducing calorific effects, is an example of the errors into 

 which an ingenious mind may be led, when eagerly 

 seeking to establish a favourite hypothesis. 



Animal and vegetable diet, which is composed largely 

 of carbon and hydrogen, passes into the digestive 

 system, and becomes converted into the various matters- 

 required for the support of the animal structure. The 

 blood is the principal fluid employed in distributing over 

 the system the necessary elements of health and vigour,, 

 and for restoring the waste of the body. This fluid, in 

 passing through the lungs, undergoes a very remarkable 

 change, and not merely assumes a different colour, but 



