ALL ORGANIC SOLIDS CONTAIN CARBON. 495 



carbonic acid, is derived from the disintegration of the solids, as 

 the great difference in the daily excretion of urea between that 

 of carnivorous and omnivorous, and that of herbivorous animals 

 shows. On the contrary, in herbivorous and omnivorous animals 

 there is the distinct kind of food termed calorifacient or non- 

 riitrogenised food, the carbon of which, after various changes 

 within the body, by combining with the oxygen received in 

 respiration, maintains the animal temperature, or, being con- 

 verted into fat, becomes deposited in the adipose tissue. The 

 case of an animal receiving an excess of food is in the mean 

 time excluded, it being assumed that all the food is put to 

 its proper uses. 



Thus, if it be ascertained how much heat has disappeared 

 in the production of a mechanical effect, then it can be pro- 

 nounced what that mechanical effort is equal to for example, 

 under the denomination of pounds raised to the height of one 

 foot ; or if it be ascertained how much mechanical effort has 

 been expended under a similar denomination, then it can be 

 pronounced how much heat has been produced. 



Dr Playfair's views coincide with those of Liebig, and though 

 in a few points we may find it necessary to differ from him, 

 we have judged it preferable to retain his leading principles on 

 this subject, notwithstanding some recent experiments that, in a 

 certain degree, seem to contradict them ; because we are satisfied 

 that further inquiry will show his conclusions to be more con- 

 sonant than the opposite to the established laws of physiology. 



Whenever oxygen unites with carbon in the living body, heat 

 is produced ; but it is an axiom in physiology that as often as 

 a living act takes place, the organic agents concerned become 

 disintegrated; and as all organic agents contain carbon, and 

 such disintegration always happens in the presence of oxygen 

 supplied by the blood, carbonic acid, and therefore heat, are 

 uniformly produced in all living acts, whether falling under 



