CHAPTER VII. 



FOOD. 



IK order that life may be maintained it is necessary that th% 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. And to arrive at a reasonable estimation 

 of the proper diet in twenty-four hours it is necessary to consider the 

 amount of the excreta daily eliminated from the body. The excreta con- 

 tain chiefly carbon, hydrogen, oxygen, and nitrogen, but also 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 the prin- 

 cipal part in forming the excreta, in large amount. We have seen in the 

 last Chapter that carbonic acid and ammonia, i.e., the elements carbon, 

 oxygen, nitrogen, hydrogen, are given off from the lungs. By the excre- 

 tion of the kidneys the urine many elements are discharged from the 

 blood, especially nitrogen, hydrogen, and oxygen. In the sweat, the ele- 

 ments 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 represented in the 

 following way (Landois) : 



Water. C. H. K O. 



By the lungs . . 330 248-8 ? 651.15 



By the skin . . 660 2.6 7 '2 



By the urine . . 1700 9 -8 3*3 15-8 11-1 



By the faeces . . 128 20- 3' 3' 12 



Grammes 2818 281*2 6-3 18 -8 681-41 



To this should be added 296- grammes water, which are produced by 

 the union of hydrogen and oxygen in the body during the process of oxi- 

 dation (i.e., 32-89 hydrogen and 263.41 oxygen). There are twenty-six 

 grammes of salts got rid of by the urine and six by the fasces. As the 



