

RESPIRATION. 119 



which the air is introduced into the body. It will now be necessary 

 to describe the changes that take place there. The atmospheric 

 air, when it goes into the lungs, is composed of about four parts 

 of a gas called nitrogen, and one part of another gas called 

 oxygen, (a small quantity of carbonic acid in the air). But 

 the air which comes out from the lungs is not the same in com- 

 position, for a considerable quantity of oxygen is found to have 

 disappeared, and in its stead we find another gas, called carbonic 

 acid, which is produced by the union of a portion of oxygen with 

 the carbon which forms a large ingredient in the composition of the 

 blood and of the body in general. Carbonic acid is a gas which is 

 fatal to animal life, and it is therefore discharged from the lungs. 

 IT an animal is made to inhale it, insensibility and death follow in 

 a very few minutes. We have already seen that the venous blood 

 is equally a poison to the animal body, and it is this same carbon, 

 or charcoal, that makes it noxious. It appears that about forty-five 

 thousand cubic inches of oxygen are consumed by an ordinary man 

 in twenty-four hours, and that forty thousand inches of this gas go 

 to form the carbonic acid produced during the same period, the re- 

 mainder of the oxygen probably combining with other ingredients 

 of the blood. This union causes animal heat similar to the 

 burning of fuel. If so the lungs and arteries are a fire-place or 

 stove which constantly generate heat. Under different circum- 

 stances, however, the consumption of oxygen varies. It is con- 

 siderably greater when the temperature is low than when it is high, 

 and during digestion the consumption has been found one-half 

 greater than when the stomach is empty. By violent exercise, 

 when the stomach is empty, it has been found to be augmented to 

 three times its usual quantity, and to four times its usual quantity 

 when food has been taken after this. 



When we thus see the great quantity of pure atmospheric air 

 which a single individual requires to carry off the noxious parts of 

 the venous blood, and to convert this into arterial blood, we can 

 easily comprehend why such dreadful consequences should follow 

 the breathing of a highly vitiated atmosphere. The most melan- 

 choly instance of this kind on record, is the well-known one that 

 occurred in the Black Hole at Calcutta. In this dungeon, 

 eighteen feet square, and having only two small windows on the 

 same side to admit air, one hundred and forty-six men were im- 

 mured. In six hours ninety-six of them had died from suffocation, 

 after the most horrible sufferings ; and in the morning, when the 



