1310 PHYSIOLOGY 



The very small variations presented by the body temperature in 

 mammals, even under the influence of considerable variation in 

 external temperature, or in the production of heat in the body, connotes 

 an accurate adaptation between the production of heat in the body 

 and the loss of heat from the body. The regulation of the temperature 

 can be effected either by regulation of heat production, by alteration 

 in the rate of loss of heat, or by a combination of both mechanisms. It 

 will be convenient to deal with these two methods of regulation under 

 separate headings. 



THE PRODUCTION OF HEAT IN THE BODY 



The reactions mainly responsible for heat production in the body 

 are those associated with oxidation ; the processes of disintegration, 

 such as are effected by means of hydrolytic ferments, accounting for 

 a very small part of the heat evolved. 



In these processes of oxidation all the organs participate, the 

 most important, especially in relation to the regulation of heat pro- 

 duction, being the skeletal muscles. These represent more than 

 half of the total weight of the soft tissues of the body, and even during 

 rest are the seat of oxidative processes and therefore of heat forma- 

 tion. Heat formation varies with the state of tone of the muscles, 

 and is largely increased with every active contraction. The effect of 

 muscular activity on the total output of energy of the body is well 

 represented in the Table given on p. 715. 



It is probable that, in relation to their size at any rate, the glands 

 are still more effective as heat producers. The liver, and the blood 

 flowing from the liver, have been stated to present a higher tempera- 

 ture than any other part of the body. On the other hand, the nervous 

 system, although dependent on a constant supply of oxygen for its 

 activities, does not appear to be the seat of extensive metabolic 

 changes, nor does the heat produced in this system play any great part 

 in maintaining the temperature of the body. 



The skeletal muscles are controlled by the central nervous system ; 

 if separated from their centres in the cord they become flaccid and 

 rapidly atrophy. The heat production in the muscles is therefore 

 also dependent on their connection with the central nervous system. 

 If this connection be severed either by curare or section of the cord, or 

 if the reflex play of impulses on the muscles be abolished by anaes- 

 thetics, the animal will react like a cold-blooded animal. The total 

 metabolism of the body and the total production of heat sink to a 

 minimum, and are diminished by application of cold, or increased by 

 application of warmth, to the surface of the body. On the other hand, 

 in the intact animal changes of temperature in the environment pro- 

 voke, reflexly by their action on the muscles, changes in the opposite 



