THE TEMPERATURE OF THE BODY 1171 



observed in men of all races and of all climes under most varying conditions 

 of food and activity. 



Just as there are limits to the power of the organism to regulate its 

 temperature when there is an excessive formation of heat in the body, so 

 there are limits to the regulation of temperature to severe alterations in the 

 temperature of the external medium. Thus if the body is subjected to 

 excessive external cold, or the loss of heat be increased by absence of clothes, 

 by depriving an animal of its fur, or by immersion in a cold bath, the tempera- 

 ture of the body may sink continuously. This fall of temperature in the 

 higher animals is very soon followed by paralysis of the highest nerve-centres 

 and loss of consciousness. The centres in the medulla are later on affected, 

 so that the respiration is slowed and the blood-pressure falls. If the tem- 

 perature does not fall too low it is possible to revive the animal or man by 

 checking the loss of heat or by supplying artificial warmth. Recovery has in 

 fact been observed in men in whom, as a result of exposure, the body tem- 

 perature had fallen to 24 C. In the same way exposure to extreme heat, 

 especially associated with muscular exercise and increased production of 

 heat in the body, may cause a rise of the body temperature. A man, or 

 animal, whose temperature is raised above the normal, is said to be in a 

 state of pyrexia. A rise of 2 or 3 C. is associated with all the phenomena 

 which characterise fever, i.e. quickening of pulse and respiration, malaise, 

 headache, and loss of muscular power. If the temperature rise to a greater 

 degree than this the patient may lose consciousness, and death ensues at a 

 temperature of about 44 C. 



The very small variations presented by the body temperature in mam- 

 mals, even under the influence of considerable variation in external tempera- 

 ture, or in the production of heat in the body, connotes an accurate adapta- 

 tion 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 production, 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 ol heat formation. Heat formatipn varies with the 

 state of tone of the muscles, and is largely increased with every active con- 

 traction. The effect of muscular activity on the total output of energy 

 of the body is well represented in the Table given on p. 639. 



