98 MANUAL OF PHYSIOLOGY. 



raised, but not quite to boiling point, in order that as much as 

 possible of the soluble materials may be extracted, and a tasteless 

 friable muscle tissue remains ("bouilli"). As the fluid is gener- 

 ally allowed to boil in order to clear it, much of the proteid ma- 

 terial which was dissolved in the earlier stage, is coagulated and 

 removed with the scum. Although "stock" cannot contain any 

 great proportion of the most important constituents of meat, it is 

 of much value as a nutriment in medical practice, possibly on 

 account of some stimulating action of its ingredients upon the 

 motions of the intestines and heart. A strongly albuminous ex- 

 tract of meat, "beef-tea," may be made by digesting flesh in a 

 small quantity of water, and keeping the temperature below that 

 at which albumin coagulates, and adding vinegar and salt to 

 facilitate the formation of syntouin and the solution of myosin. 

 The salt can be then removed by dialysis. 



Eggs. Eggs consist of two parts, one the white, composed of 

 albumin, and the other, the yolk, chiefly made up of fat. 



The white is a concentrated watery solution of albumin, held to- 

 gether by delicate structureless membranous meshworks. Besides 

 the albumin it contains traces of fat, sugar, extractives, and salts. 



The yellow fat emulsion of the yolk contains a peculiar proteid, 

 vitellin, some grape sugar, and some inorganic salts, in which 

 combinations of phosphoric acid and potassium are conspicuous. 

 Raw eggs are difficult of digestion, as is all uncooked albumin. 

 Hard boiled eggs, if not finely divided by mastication, are also 

 very difficult to digest, for the gastric juice cannot penetrate the 

 hard masses of coagulated albumin which are so easily and com- 

 monly swallowed. Eggs, when lightly cooked, are easily digested, 

 as the albumin is already coagulated, and cannot be introduced 

 into the stomach in large masses. Eggs are of very great nutritive 

 value, as they contain so large a percentage of proteid, fats and salts. 



Vegetable Food. Vegetables differ from animal food : 



(1.) In containing a much greater proportion of material which 

 for man is indigestible (cellulose), and a less proportion of real 

 nutritive material. 



(2.) The percentage of proteid is below that of animal food, 

 and the proportion of carbohydrates is generally much greater, 



