ANIMAL HEAT. 183 



fire burns languidly in the bodies of the people, they are 

 not well warmed, and their sensations persuade them that 

 the room is growing cooler. 



427. The narrow-chested are colder than the broad- 

 chested ; the tight-bound, than the loosely-dressed ; and those 

 who breathe the impure air of close arid unventilated rooms, 

 than those who breathe the free air of the fields. The former 

 need more external protection of houses or clothing, or more 

 outward heat from fires, than the others. A free expansion 

 of the chest, with a good supply of pure air, is, therefore, an 

 economy of clothing and of fuel. When the air is dense 

 and heavy, as when cooled, it contains a greater weight of 

 oxygen to the cubic inch, than when it is rare and light, as 

 when heated. We therefore breathe more oxygen in winter 

 than in summer, and the fire, consequently, burns most ac- 

 tively when it is the most needed. 



428. Fuel, as well as air, is necessary to keep up this 

 internal combustion in the animal body. This is supplied by 

 the atoms of wasted flesh that have died in the various tex- 

 tures, and are ready to be burned or combine with oxygen, and 

 need to be carried away. The combustible matters of the 

 flesh its carbon and hydrogen are originally supplied by 

 the food that contains the same materials. These elements 

 of the food, being converted first into chyle, then into blood, 

 arid next into flesh, are at last burnt by their union with 

 oxygen, and carried out through the veins and the lungs. 

 As the food is the only source from which this fuel is sup- 

 plied, of course, all other things being equal, the internal 

 fire must burn, and the body be warmed, in proportion to the 

 amount of carbon and hydrogen which is eaten, and incor- 

 porated into and becomes a part of the tissues. 



429. The well-fed and well-nourished, those who live 

 upon good and generous food, having a better supply of 

 fuel, are therefore better warmed than the hungry, or those 

 who live upon a poor and meagre diet. The traveller who 

 has been long exposed to the severe weather without eating, 

 in winter, complains that he is both hungry and cold. His 



