XX INTRODUCTION. 



Throughout this I have laboured to attain a 

 knowledge of those conditions of the system which 

 promote or retard the generation of animal heat, 

 and these have little connexion with any par- 

 ticular theory. The present view may therefore 

 be considered as an important addition to what 

 has been already said on the cause of animal 

 heat. The explanation I shall propose goes far 

 to support the doctrine of BLACK, in which the 

 increase of heat is attributed to chemical changes 

 in the lungs. It is now, I believe, almost uni- 

 versally allowed, that the arterial is warmer than 

 the venous blood, and it is more than probable 

 that this result depends on chemical action. 

 By taking into consideration, that a small quan- 

 tity only of the air within the lungs is at any one 

 moment deteriorated, and, still further, that the 

 left ventricle contracts 70 or 80 times per minute, 

 in order to propel the arterial blood which is 

 transmitted by the lungs, we shall have reasons 

 sufficiently ample to account for the possibility 

 of these organs bearing such changes, and for the 

 ease with which the system is supported in an 

 equable temperature. If the body be supposed 

 to possess 30 pounds of blood, and the heart to 



