302 THE HUNAN BODY. 



the broth, by putting the raw meat at once into boiling 

 water, which coagulates the surface albumin before it dis- 

 solves out, and this keeps in the rest. In any case the 

 myosin, being insoluble in water, remains behind in the 

 boiled meat. In baking or roasting, all the solid parts of 

 the flesh are preserved and certain agreeably flavored bodies 

 are produced, as to the nature of which little is known. 



Eggs. These contain a large amount of egg albumen 

 and, in the yolk, another proteid, known as vitellin. Also 

 fats, and a substance known as lecithin (p. 14), which is 

 important as containing a considerable quantity of phos- 

 phorus. 



Milk contains a proteid, casein; several fats in the hitler; 

 a carbohydrate, milk sugar; much water; and salts, espe- 

 cially potassium and calcium phosphates. Butter consists 

 mainly of the same fats as those in beef and mutton; but 

 has in it about one per cent of a special fat, butyrin. In 

 the milk it is disseminated in the form of minute globules 

 which, for the most part, float up to the top when the milk 

 is let stand and then form the cream. In this each fat 

 droplet is surrounded by a pellicle of albuminous matter; 

 by churning, these pellicles are broken up and the fat drop- 

 lets run together to form the butter. Casein is insoluble in 

 water; in milk it is dissolved by the alkaline salts present. 

 When milk is kept, its sugar ferments and gives rise to 

 lactic acid, which neutralizes the alkali and precipitates the 

 casein as curds. In cheese-making the casein is similarly 

 precipitated by the addition of an acid, and (the whey being 

 pressed out) it constitutes the main bulk of cheese. 



Vegetable Poods. Of these wheat affords the best. In 

 1000 parts it contains 135 of proteids, 568 of starch, 46 of 

 dextrin (a carbohydrate), 49 of grape sugar, 19 of fats, 

 and 32 of cellulose, the remainder being water and salts. 

 The proteid of wheat is mainly gluten, which when moist- 

 ened with water forms a tenacious mass, and this it is to 

 which wheaten bread owes its superiority. When the 

 dough is made yeast is added to it, and produces a fermen-' 

 tation by which, among other things, carbon dioxide gas 

 is produced. This gas, imprisoned in the tenacious dough. 



