58 THE CHEMISTRY OF FOOD. 



16. They likewise decompose, or putrefy, under the influ- 

 ence 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 occasion- 

 ally borne by the icebergs to the coast of Siberia, com- 

 pletely 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. 



18. Fibrin is derived from meats, and exists in the 

 blood both of man and the lower animals. Gluten, or 

 vegetable fibrin, resembles closely true fibrin, and is abun- 

 dantly furnished in wheat and other grains from which 

 flour is commonly made. Animal fibrin coagulates spon- 

 taneously when it is removed from the body, and thus 

 causes the "clotting" of the blood. 



19. Casein is the curdy ingredient of milk, and a highly 

 important food-substance. Its coagulation in milk takes 

 place not from heat, but by the addition of an acid, and 

 also when milk becomes sour from exposure to the air. It 

 is commonly effected, however, by introducing a piece of 

 rennet, a preparation made from a calf's stomach. The 

 curds, or casein, may then be separated from the wliey, 



1 6. Decomposition ? Effect of cold ? Illustrations ? Elephants ? 



17. In what substance!* does albumen exist ? What further is said of the e<*s * 



18. Fibrin, gluten, clotting of the blood ? 



19. Casein ? Its coagulation ? Effect of rennet ? Making of cheese? 



