410 PROPERTIES AND FUNCTIONS 



than in birds or quadrupeds, for being situated in a fluid 

 whose specific gravity is nearly equal to that of their 

 bodies, it must require much less muscular exertion to 

 move in that fluid than in the air or upon the surface of 

 the earth. 



Experiments have proved that full grown persons 

 respire twentyfour thousand cubic inches of air per hour, 

 or five hundred and ninetysix thousand per day. We 

 will suppose that each time the heart contracts it throws 

 one half ounce of blood to the lungs, which, by the way, 

 is a small calculation : now we know that the heart con- 

 tracts on an average about seventy times in a minute ; 

 thus thirtyfive ounces of blood must be sent from ihe 

 heart to the lungs per minute, making more than 120 

 pounds per hour, or 2880 pounds per day. Therefore 

 the air cells, which are extremely delicate, in the course 

 of twentyfour hours sustain the weight of about thirtynine 

 hogsheads of air, and the minute blood vessels 2880 

 pounds of blood in the same length of time. 



This estimate will give you some idea of the wonderful 

 power which these tender organs possess, and of their 

 importance in the animal economy. In man there is a 

 strong and intimate connexion between the heart and 

 lungs. If we cease to respire the heart ceases to act, or 

 if the blood does not undergo its proper change in the 

 lungs, that is, if it is not changed from a dark to a light 

 red, or more properly, if it is not decarbonized, all the 

 organs of the body as it were, immediately take cognizance 

 of it, the heart ceases to act and the man dies. The 

 question may be asked, how the bloed coming in contact, 

 or nearly so, with the air, can be so powerfully operated 

 upon as that this change shall take place. 



We know that this change does take place, and we 

 know also that we cannot exist unless it does; but how 

 this is effected, what is the power or mode by which it is 

 done, we know not. We can only say that it is a vital 

 process performed by a vital power. It surely has been 

 supposed that the oxygen of the atmosphere and the car- 

 bon in the dark or venous blood, when coming in contact) 

 or nearly so, united, and thus formed carbonic acid gas, 

 which was expelled from the lungs at each expiration. 



