ANIMAL HEAT. 181 



consequently, every part of the body is warmed. The more 

 rapid is the circulation and the more frequent are the 

 changes of living for dead particles, the more carbon and 

 hydrogen are burnt, and the greater is the heat given out. 

 Whatever increases the interchange of particles, the work of 

 absorption and nutrition, and consequently the flow of blood, 

 increases the internal fire and the evolution of heat. Motion 

 is attended with greater waste of particles, and, of course, 

 with greater absorption of carbon and hydrogen, ( 127, p. 

 61,) and greater development of heat. Labor, therefore, 

 warms the body, and, if violent, may heat it uncomfortably. 

 The watchman keeps himself warm with exercise, and the 

 passenger leaves the vehicle to warm his feet with running. 

 The hardy laborer heats himself with his exercise, and sits 

 down quietly to cool his body. ^ 



423. On the contrary, whatever interrupts the circulation 

 and the interchange of particles prevents the development of 

 heat. If we bind up the arm or finger with a tight cord, 

 and prevent the flow of the blood through it, the limb be- 

 comes cold. It is a common and a true observation, among 

 shoemakers, that a loose boot is warmer in winter than a 

 tight one, because the latter presses upon the blood-vessels, 

 and interrupts the full flow of blood. So we find, if one 

 side or one limb be palsied, that side or that limb becomes 

 cold, for the same reason. 



424. This animal heat then, is sustained by the combus- 

 tion of the dead atoms of the flesh in all the parts of our 

 frames where the blood circulates. In order to maintain 

 this combustion, the same things are requisite that are 

 needed to support fire elsewhere ; these are fuel and air. 

 To deprive the body of either would be as fatal to its internal 

 heat as taking away the fuel or the air would be to the fire 

 of the stove. As the wood in the fireplace burns by aid of 

 the oxygen which it derives from the air, and as this fire 

 burns freely in proportion to the quantity of air which it 

 receives, so the internal fire of the animal body, deriving its 

 oxygen from the air, burns in proportion to the fulness of its 



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