CHAPTER VI. 



FOODS AND DIET. 



IN order that life of the individual may be maintained it is neces- 

 sary that his body should be supplied with food in proper quality and 

 quantity. 



The food taken in by the animal body is used for the purpose of re- 

 placing the waste of the tissues. In order to arrive, therefore, at a 

 reasonable estimation of the proper diet required in the twenty-four 

 hours, it is essential that we should know the amount and composition 

 of the excreta daily eliminated from the body. Careful analysis of the 

 excreta shows that they are made up chiefly of the chemical elements, 

 carbon, hydrogen, oxygen, and nitrogen, but that they also contain to a 

 less extent, sulphur, phosphorus, chlorine, potassium, sodium, and 

 certain other of the elements. Since this is the case it must be evident 

 that, to balance this waste, foods must be supplied containing all these 

 elements to a certain degree, and some of them, viz., those which take a 

 principal part in forming the excreta, in large amount. 



Of the excreta we have seen in the last Chapter that carbonic acid 

 and ammonia, which are made up of the elements, carbon, oxygen, 

 nitrogen, hydrogen, are given off from the lungs. By the excretion of 

 the kidneys the urine many elements are eliminated from the blood, 

 especially nitrogen, hydrogen, and oxygen. In the sweat, the elements 

 chiefly represented are carbon, hydrogen, and oxygen, and also in the 

 faeces. By all the excretions large quantities of water are got rid of 

 daily, but chiefly by the urine. 



The relations between the amounts of the chief elements contained 

 in these various excreta in twenty-four hours may be thus summarized: 



