THE CHEMISTRY OF FOOD. 57 



most of the vegetables, and is a very important component 

 of animal tissues. It enters into the composition of hu- 

 man blood in about one part per thousand. Ordinarily, 

 the food conveys to the system enough iron for its use, but 

 it must sometimes be introduced separately as a remedy, 

 especially after great loss of blood, or after some wasting 

 disease. Under its influence the blood seems to be 

 rapidly restored, and a natural color of the lips and skin 

 replaces the pallor caused by disease. 



13. Other Inorganic Substances. In addition to 

 the substances mentioned, the mineral kingdom supplies 

 compounds of soda, potash, and magnesia, which are es- 

 sential for the use of the body. They occur in small 

 quantities in the body, and enter it in combination with 

 the various articles of diet. 



14. Organic Substances. These substances are derived 

 from the vegetable and animal creations. They comprise 

 all those articles which are commonly spoken of as " food," 

 and which are essential to sustain the body in life and 

 strength. They are divided into three groups, namely: 

 the Albuminoid substances, the Fats, and Sugars. 



15. The Albuminoids. This class includes three im- 

 portant nutritive substances (1) Albumen, which gives it 

 its name; (2) Fibrin, including gluten; and (3) Casein. 

 These compounds constitute a large part of the human 

 body, and the food contains them in proportionally large 

 quantities. Their importance is so great, and the system 

 so promptly suffers from their absence, that they have been 

 styled the " nutritious substances." The properties which 

 they hold in common are, that they do not crystallize, and 

 have a jelly-like form, except when heat is applied to them, 

 when they harden, or coagulate. 



1 3. Soda, potash, and magnesia ? How do they occur ? 



1 \. Onranic eubstances, whence derived ? What do they comprise ? Groups :. 

 li. The Albuminoid class, includes what? These compounds conatituta 

 what? The food '? Their importance? Their properties ? 



3* 



