428 ANIMAL HEAT. [CHAP. XXX. 



jecture only. It may be regarded as most probable that the 

 chemical changes which issue in the formation of carbonic acid and 

 water, and the disengagement of heat, are effected in the tissues 

 themselves, or in the systemic capillaries, in the immediate vicinity 

 of the tissues. 



Influence of the Nervous System. Much difference of opinion has 

 existed as to the share taken by the nervous system in the pro- 

 duction and maintenance of animal temperature, some distinguished 

 men having argued that this system is in some way the source of 

 heat, while others have limited its operation to the exercise of a 

 controlling and regulating influence over this important function. 

 The latter conclusion is that to which a just estimate of the 

 numerous facts advanced on both sides would appear to lead. 

 The experiments of Dulong, repeated and modified by Despretz, 

 seemed, indeed, for some time to indicate that a portion of the 

 heat developed in the body could not be referred to the consump- 

 tion of the oxygen inhaled, and that, therefore, some other source 

 for it must be sought. They compared the heat given to a calori- 

 meter by an animal placed within it, with that produced by the 

 combustion out of the body of as much carbon and hydrogen as 

 the animal gave off in the same time, in the form of carbonic acid 

 and water, and found that more heat was given off by the animal 

 than the chemical products of its respiration would account for, 

 to the extent of from one-fifth to one-tenth. It has since been 

 shown, however, that, on the one hand, allowance was not made 

 for an actual cooling down of the animal below its normal tem- 

 perature by exposure to the refrigerating influence of the calori- 

 meter, so that the heat indicated had not all been produced within 

 the period of the experiment ; and, on the other, that the heat 

 generated by the corresponding chemical actions put of the body 

 had been under-estimated. Dulong himself furnished a more 

 correct estimate of the heat developed by the combustion of 

 hydrogen; and his results have been confirmed by Fabre and 

 Silbermau. Hence, while it would be premature to attach too 

 much value to such experiments, considering our ignorance of thf 

 exact series of chemical changes indicated by the resultant carbonic 

 acid and water, they certainly are not, as they once seemed to 

 opposed to the chemical theory of animal heat. 



It may be regarded as certain, that the nervous system exerts 

 considerable influence upon the development of heat in the body. 

 The experiments of Sir Benjamin Brodie, and subsequently those 

 of Le Gallois and Chossat, have established the fact that lesioi 



