106 MANUAL OF PHYSIOLOGY. 



an extract of calves' stomach which, without the presence of 

 any acid, curdles milk and draining off the solution of milk 

 sugar and salts (" whey "). It contains most of the proteid, and 

 a great deal of the fat of the milk. During the ripening of the 

 cheese more fat is formed, apparently from the proteid, while leucin 

 and tyrosin also appear. 



Meat. We use the flesh of the vegetable-feeding mammals 

 and birds that are must easily obtainable, and many kinds of 

 fish. The invertebrate animals, mostly shell-fish, need hardly 

 be mentioned in a physiological dietary, and are not spoken 

 of as meat. 



As it comes from the butcher, meat consists of many of the 

 animal tissues, the chief ones being flesh (muscle tissue), fat and 

 some sinews (fibrous tissue). The fleshy or lean part of meat is 

 chiefly made up of nitrogenous materials, and contains : (1) Sev- 

 eral proteids, chiefly the globulin, myosin ; (2) gelatine-yielding 

 substances ; (3) carbohydrates, and sugar, and possibly still some 

 glycogen ; (4) small quantities of fat ; (5) several inorganic 

 salts ; (6) extractives. 



Meat may be eaten raw, but as it is impossible to impart to it 

 the various flavors which our artificial tastes demand without 

 some special preparation, it is generally cooked before use. More- 

 over, the not infrequent occurrence in muscle of parasites which 

 would prove injurious if swallowed alive, makes the exposure of 

 meat to a temperature high enough to insure their destruction 

 advisable. 



Apart from pleasing the taste, it is of great importance so to 

 prepare meat as to preserve in it all the nutrient parts, many of 

 which are soluble in water, and therefore are apt to be removed 

 if that solvent be injudiciously used. Thus, the process of roast- 

 ing, in which all its nutrient parts are retained, ought to be more 

 satisfactory than boiling, by which the salts, extractives, carbo- 

 hydrates, gelatine, and some albumin may be dissolved by the 

 water. However, if the meat be plunged into water which is 

 already boiling, the proteids near the surface are rapidly coagu- 

 lated, and the water cannot reach the central parts in sufficient 

 quantity to remove even the soluble ingredients. The whole of 



