THE BLOOD. 495 



almost to zero. This, however, only shows that the more 

 active the change between the blood hence the body and 

 air, the larger the quantity of heat developed. 



The production of animal heat is affected by the nervous 

 system. Sir Benjamin Brodie noticed in the human subject, 

 and other observers in the lower animals, that the higher 

 the spine is affected by injury or disease, the greater the 

 extent to which the body cools. It has been remarked that, 

 immediately after the division of a nerve, the temperature of 

 the part to which that nerve is distributed is increased, but 

 this is due to a morbid change such as congestion or 

 inflammation. Thus, on division of the fifth pair of nerves, 

 the eye is apt to inflame, and symptoms of catarrh also 

 manifest themselves. Sir Everard Home and Elliotson 

 showed that ultimately there was a loss of temperature in all 

 parts deprived of nervous influence by section of the nerves. 

 Division of the median nerve has been observed to lead to a 

 reduction in the temperature of the hand, and these cases 

 demonstrate how heat is generated in all parts of the system. 



" .Ajiimal heat," says Dr Dalton, " is a phenomenon which 

 results from the simultaneous activity of many different pro- 

 cesses, taking place in many different organs, and dependent, 

 undoubtedly, on different chemical changes in each one. The 

 introduction of oxygen and the exhalation of carbonic acid 

 have no direct connection with each other, but are only the 

 beginning and the end of a long series of continuous changes, 

 in which all the tissues of the body successively take a part. 

 Their relation is precisely that which exists between the 

 food introduced through the stomach, and the urinary ingre- 

 dients eliminated by the kidneys. The tissues require for 

 their nutrition a constant supply of solid and liquid food 

 which is introduced through the stomach, and of oxygen 

 which is introduced through the lungs. The disintegration 



