342 Comparative Physiology. 



formed the subject of much discussion. When carbonic acid is 

 formed a great condensation of bulk takes place, the carbonic 

 acid not being near so bulky as the oxygen and carbon ; and, as 

 the particles of caloric or heat are repellent and expansive, it is 

 said condensation of bulk is always accompanied by heat ; and 

 the principal, some say the only, source of heat is in the function 

 of respiration, by which oxygen is inhaled to be converted into 

 carbonic acid in the system. The carbonic acid occupies less 

 bulk than the oxygen and carbon, and the bulk being condensed 

 caloric is developed, from the latent state it becomes sensible. 

 It has been said, however, that the computed effects of the 

 quantity of oxygen inspired are not sufficient to counterbalance 

 the waste of heat in animals, by the various ways in which it is 

 given off by the body ; and some say the motions of the body 

 form the source of heat, while others assert that it springs from 

 the nervous system, all the motions of which, they say, are 

 accompanied with electricity, which developes heat. Sir J. 

 Herschel has likened the successive discharges from a galvanic 

 battery, fitted up so as to give off the electricity as it accumu- 

 lates, to the pulsations of the heart. It has not been shown, 

 however, how motion produces heat unless by condensation ; and 

 electrical and chemical processes are so much combined that the 

 one is seldom found without the other. Dr. Carpenter seems to 

 consider the source of heat in animals as still undecided. Pro- 

 fessor Miiller, in the newly published translation of his works 

 by Dr. Baly, considers the experiments of Brodie, in which 

 artificial respiration was kept up in rabbits after death had been 

 caused by destruction of the nervous system, and in which 

 carbonic acid was given off as during life without maintaining the 

 heat of the body, a convincing proof that respiration is not the 

 sole cause of heat. He says (p. 86.) : " Several of the facts we 

 have mentioned prove that the influence of the nerves in the 

 organic processes of the body contributes greatly to the produc- 

 tion of animal heat in other parts than the lungs. Berzelius is 

 also of this opinion, and it seems to derive confirmation from the 

 rapid and momentary increase of temperature, in states of 

 nervous excitement caused by the passions of the mind." Pro- 

 fessor Liebig, in his Animal Physiology, which, like the Agri- 

 cultural, abounds in concise and mathematical statements on the 

 most abstruse subjects, seems to consider respiration as sufficient 

 to produce all the heat needed, by furnishing the oxygen which 

 is condensed into carbonic acid by carbon, and into water by 

 hydrogen. The force by which nervous power acts, he says, is 

 chemical ; when the nervous power is destroyed, the oxygen 

 inhaled does not meet with these substances with which, in the 

 normal state, it would have combined. He takes no notice of 

 the experiments of Brodie, in which artificial respiration, though 

 the oxygen combined with carbon as usual, and carbonic acid 



