ORGANS OF CIRCULATION AND RESPIRATION. 47 



of the blood through them. This union is a simple burning of 

 carbon and hydrogen ; that is, these gases each unite with oxygen, 

 just as our coals and gas do in our own dwellings; and the lungs 

 are as much a stove as any in our houses, the only difference being 

 that the burning is more gradual, and, consequently, the tempera- 

 ture is not raised high enough to give out light, and a moderate 

 heat. In a state of muscular repose, therefore, the only office 

 of the lungs is to burn off the superfluous carbon, and thereby 

 maintain the proper temperature of the whole body, by warming 

 the blood which is then equally diffused, and this carbon is 

 continually afforded either by the regular supplies of food, or, 

 failing this, by the fat of the body. But, over and above this 

 heat-maintaining process, they also serve to burn up the carbon 

 which results from the wear and tear of the muscles, bones, &c., 

 and which, during violent exercise, is poured into the blood in 

 enormous quantities. It appears now to be well ascertained that 

 every contraction of a muscle is accompanied by the loss of a part 

 of its elements, large or small, according to the degree of its 

 action and the same is most probably the case with the brain 

 and all other organs when in activity. The moment, therefore, 

 the muscles are put into violent action, whether those of the 

 limbs, or the trunk, or even the heart itself, increased quantities 

 of carbon are poured into the blood. This fluid, thus as it were 

 overflowing with carbon, circulates through the lungs and occasions 

 the feeling of distress which instinctively calls for more air in order 

 to burn it off, and thus keep the blood in a state of purity. The 

 electric telegraph (the nerves of sensation) is set in motion, the 



