80 THE CHEMISTRY OF FOOD 



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 sub- 

 stances, the Fats, and Sugars. 



15. The Albuminoids. This class includes three important 

 nutritive substances (1) Albumen, which gives it its name ; 

 (2) Fibrin, including gluten; and (3) Caseine. These com- 

 pounds 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. 



16. They likewise decompose, or putrefy, under the influence 

 of warmth, and moisture. Hence the decay of all dead animal 

 tissues. Cold arrests this process. It is well known that 

 milk, eggs, and the like, " keep " much, longer in winter than 

 at other seasons. The bodies of elephants, caught in the ice 

 many hundred years ago, are occasionally borne by the icebergs 

 to the coast of Siberia, completely frozen, but preserved almost 

 perfectly in form and limb. 



17. Albumen exists in milk, meat, the grains, and the juices 

 of many plants; but the purest form is obtained from the 

 white of egg. When we consider that an egg is composed 

 chiefly of albumen and water namely, six parts in seven ; 

 and when we also consider the numerous, diverse, and complex 

 tissues the muscles, bones, internal organs, bill, claws, and 

 feathers with which the chick is equipped on leaving his 

 shell, we are impressed with the importance of these apparently 

 simple constituents of the food and body. (Head Note 7.) 



7. Weight and Health. "The weight of the body is very generally 

 assumed to be an infallible index or proof of the maintenance of a healthy 



15. The Albuminoid class includes what? These compounds constitute what? The 

 food ? Their importance ? Their properties ? 



16. Decomposition? Effect of cold? Illustrations? Elephants? 



17. In what substances does albumen exist ? What further is said of the egg ? 



