FOOD UNDERGOES COMBUSTION IN THE BODY. 1*7 



what form have they been expelled from the body ? Carbon and 

 hydrogen have been furnished to the body, and yet the weight of 

 the body, with respect to these elements, has not increased : the 

 body has received in the food a quantity of alkalies and of phos- 

 phates, but still the amount of these substances in our body has 

 not been rendered greater. 



These questions are easily solved, when it is considered that 

 the food does not. supply the only conditions necessary for the 

 support of the vital processes, for there are other conditions 

 which distinguish animals essentially from plants. 



The life of an animal is essentially connected with a continual 

 introduction into its system of the oxygen contained in air. 

 Without ah* and oxygen, animals cannot exist. In the process of 

 respiration, a certain quantity of oxygen is introduced into the 

 blood by means of the lungs. The air which we respire contains 

 this oxygen, and yields it to the constituents of the blood ; the 

 blood of an adult man removes from the air, at each respiration, 

 about two cubic inches of oxygen. A man consumes in 24 hours, 

 from 10 to 14 ounces of oxygen — in a year, hundreds of pounds ; 

 what then becomes of this oxygen ? We take into our bodies 

 pounds weight of food and pounds weight of oxygen, and never- 

 theless the weight of our body either does not increase to any 

 sensible extent, or it does so in a much smaller proportion than 

 corresponds to the food : in certain individuals (in old age) it 

 experiences a continued reduction. 



It must be obvious, that this phenomenon is explicable only on 

 the supposition that the oxygen and the constituents of the food 

 exercise on each other in the organism a certain action, in con- 

 sequence of which both disappear from the body. This is actu- 

 ally the case ; for none of the oxygen respired as a gas into the 

 body remains in it ; it is separated in the form of carbonic acid 

 and water. The carbon and hydrogen, which have combined 

 with the oxygen, are derived from the organism ; but as these ele- 

 ments of the body are obtained from the food, it may be said, 

 that, in their final form, all the elements of food capable of uniting 

 with oxygen are converted, in the living body, to oxygenized 

 compounds, or, what expresses the same thing, they enter into 

 combustion. 



