THE DAIKY 185 



reimet will not curdle milk. The enzyme, known as rennin^ 

 lab, chymosin, or 'pixine, acts best at 35° and is destroyed at 

 70° C. It is found in the stomachs of many animals, espe- 

 cially in young ones, while enzymes possessing similar pro- 

 perties have been found in birds, fishes, many plants, and i>-« 

 the products of the action of certain bacteria. 



Milk Albumin resembles blood albumin. It is in complete 

 solution in milk, but coagulates and precipitates when the 

 milk is heated to 72° C. It is readily precipitated by lead, 

 copper, or mercury salts, or by tannin or alcohol. It resembles 

 casein in composition, but contains about twice as much 

 sulphur and no phosphorus. 



Milk Sug*aP' — Lactose or lacto-biose occurs in the milk of 

 all animals, but is not present in plants. It is usually com- 

 bined with one molecule of water, as represented by the 

 formula ^x^22^ix + ^^fi- This substance crystallises in large 

 rhombic or monoclinic crystals, which lose water at about 130''. 

 It possesses a faint sweet taste, and is very soluble in hot 

 water. Milk sugar, like glucose, has strong reducing pro- 

 perties, precipitating metallic silver from ammoniacal silver 

 nitrate or cuprous oxide from alkaline copper salts. 



By the action of hot dilute acids it combines with a mole- 

 cule of water and yields a mixture of glucose and galactose, 

 isomeric bodies of the composition CIl20H(CHOIl)4.CHO. 



An enzyme known as lactase Ccin bring about the same 

 change. 



Milk sugar does not easily undergo alcoholic fermentation, 

 but very readily suffers the lactic fermentation under the 

 influence of certain micro-organisms. The change may be 

 represented thus: 



^u^tfin + HP = 4C,HX0H).C00H; 



but other products are simultaneously formed, and the reaction 

 is doubtless much more complex. This change in the milk 

 sugar is the cause of milk " going sour " when kept. The 



