CHAPTER XVI 

 ANIMAL 1 1 EAT 



The Temperature of the Body. The body of a man is 

 usually warmer than the things around him. Moreover, it is as 

 warm on a hot day as on a cold day ; the temperature is always 

 the same, lacing about 98" Fahrenheit (37 " Centigrade). This 

 may be ascertained by placing a thermometer in the armpit or 

 in the mouth for a few minutes. 



Loss of Heat. -The body is constantly losing heat. 

 I l-,it is lost, as we have just seen, from the skin by the evapora- 

 tion of the sweat, by radiation, and by conduction. A con- 

 siderable amount is also lost by the breath in warming the air 

 expired, and a very little also is lost in warming the urine and 

 the fiercs leaving the body. To make up for the heat lost 

 heat must be produced in the body, and seeing that the 

 temperature of the body docs not change, the amount produced 

 and the amount lost must be equal to each other. 



Source of Heat. The living tissues are constantly under- 

 going oxidation, and the complex substances of which they are 

 composed are breaking up into simpler substances, of which the 

 i hiefarc carbonic arid, water, and urea. Heat is formed by this 

 oxidation just as it is formed by the oxidation of coal, which 

 takes plate \\lien coal is burnt, for the complex substances of 

 the coal break up in the same way into simpler substances. 

 The heat of the body is due then to the oxidation of the 

 tissues. Some of the tissues are oxidising faster than others, 

 and so produce more heat in the same time. The muscles, 

 forming, as they do, so large a portion of the tissues of the 

 body, contribute most of the heat. Next to them in import- 

 ance come the larye solid organs, such as the liver and brain, 



