504 PHYSIOLOGY AT THE FARM. 



There still remains, however, the third point for considera- 

 tion namely, how far a correct estimate has yet been made as 

 to the amount of heat required daily to keep up the animal 

 temperature in the various circumstances of climate, and par- 

 ticularly in the common range of our own climate. If it can- 

 not be made probable that an over-estimate of the amount of 

 heat required to keep up the animal temperature has hitherto 

 been made, then the prevailing doctrine of animal heat cannot 

 be made to accord with the view belonging to the "conservation 

 of energy" namely, that a considerable part of the carbonic 

 acid thrown off by the lungs is the result of the decomposition 

 of contractile fibres ; for example, in the unceasing action of the 

 heart, and in the contraction of the locomotive muscles by 

 which bodily exertions are accomplished. It is manifestly 

 quite immaterial whether we suppose heat to be first formed 

 and then converted into vital force and into mechanical force, 

 or whether we suppose the vital and the mechanical force 

 exerted at any one period to be the direct result of the com- 

 bination of carbon and oxygen ; in either case the quantity of 

 carbonic acid thrown off in respiration is not, according to the 

 doctrine of the conservation of energy, the mere measure of the 

 heat rendered manifest, but the measure of the heat rendered 

 manifest jointly with the corresponding amount of vital force 

 and of mechanical force put forth in the mean time. 



But to come to the point to be considered. It would far 

 exceed our limits to enter upon an examination of the various 

 experiments on living animals for example, the making them 

 breathe in receivers containing air and surrounded by water, 

 by the rise in the temperature of which the amount of animal 

 temperature produced in a given time has been judged of. The 

 only kind of test for the trial of the point in question of which 

 we can venture to avail ourselves, admits but of an approxi- 

 mative determination. The animal body consists of a large 



