THE NATURE AND INFLUENCE OF FOODS. 445 



in their vital work, the leading characteristic of each kind is so 

 marked as to warrant the classification wbich Liebig has formulated. 



It is understood that the structures of the body are in a state of 

 continual change, so that atoms which are present at one hour may be 

 gone the next, and, when gone, the structures will be so far wasted, 

 unless the process of waste be accompanied by renewal. But the re- 

 newing substance must be of the same nature as that wasted, so that 

 bone shall be renewed by bone and flesh by flesh ; and hence, while 

 the body is always changing, it is always the same. This is the duty 

 assigned to food to supply to each part of the body the very same 

 kind of material that is lost by waste. 



As foods must have the same composition as the body, or supply 

 6uch other materials as by vital action may be transformed into the 

 substances of the body, it is desirable to gain a general idea of what 

 these substances are. 



The following is a summary statement of the principal materials 

 of which the body is composed : 



Flesh in its fresh state contains water, fat, fibrine, albumen, and 

 gelatine, besides compounds of lime, phosphorus, soda, potash, magne- 

 sia, silica, and iron, and certain extractives. 



Blood has a composition similar in elements to that of flesh. 



Bone is composed of cartilage, gelatine, fat, and salts of lime, mag- 

 nesia, soda, and potash, combined with phosphoric and other acids. 



Cartilage consists of chondrine, which is like gelatine in composition, 

 with salts of soda, potash, lime, phosphorus, magnesia, sulphur, and iron. 



The brain is composed of water, albumen, fat, phosphoric acid, os- 

 mazome, and salts. 



The liver consists of water, fat, and albumen, with phosphoric and 

 other acids in conjunction with soda, lime, potash, and iron. 



The lungs are formed of a substance resembling gelatine, albumen, 

 a substance analogous to caseine, fibrine, various fatty and organic 

 acids, cholesterine, with salts of soda, and iron and water. 



Bile consists of water, fat, resin, sugar, fatty and organic acids, 

 cholesterine, and salts of potash, soda, and iron. 



Hence it is requisite that the body should be provided with salts 

 of potash, soda, lime, magnesia, sulphur, iron, and manganese, as well 

 as sulphuric, hydrochloric, phosphoric, and fluoric acids and water ; also 

 nearly all the fat which it consumes daily, and probably all the nitro- 

 genous substances which it requires, and which are closely allied in 

 composition, as albumen, fibrine, gelatine, and chondrine. It can pro- 

 duce sugar rapidly and largely, and fat slowly and sparely, from other 

 substances ; also lactic, acetic, and various organic acids, and peculiar 

 extractive matters. 



So great an array of mysterious substances might well prevent us 

 from feeding ourselves or others if the selection of food depended 

 solely upon our knowledge and judgment ; but it is not so, for, inde- 



