i MILK 9 



smaller specific rotation, a [n] = 37. When milk is heated 

 to about 70 C. the albumin coagulates. Lacto-globulin w;is 

 also first prepared from milk by Sebelien, 1 who saturated milk 

 with common salt, which causes the precipitation of the casein, 

 and then added magnesium sulphate to the filtrate until 

 saturated. In its properties lacto-globulin closely resembles 

 serum-globulin, with which it is perhaps identical. 



Milk sugar or lactose, C 12 H 22 O n + H 2 O, is a disaccharide, 

 which on hydrolysis is split up into two hexose sugars, dextrose 

 and galactose. Milk sugar is only found in milk, from which it 

 is easily prepared by evaporating the whey left in cheese- 

 making, after first coagulating the protein substances by means 

 of heat. After repeated crystallisation, milk sugar is obtained 

 in the form of colourless, rhombic crystals with 1 molecule of 

 water of crystallisation. When heated to 130 140 C. } the 

 water of crystallisation is easily given up, and at 170 180 C. 

 the milk sugar passes into a brown, amorphous mass (lacto- 

 caramel) with the formula C 6 H 10 O 5 . Milk sugar dissolves in 6 

 parts cold and in 2'5 parts boiling water, and the solution is 

 only slightly sweet. In alcohol and ether, milk sugar is in- 

 soluble. The aqueous solution of milk sugar is dextrorotary, 

 and the power of rotation which is obtained constant by heating 

 the solution to 100 C. is a [D] = + 52'5. 



Ordinary yeast does not ferment milk sugar, but under the 

 influence of certain yeasts, which were discovered by Duclaux, 2 

 it can be split up into alcohol and carbon dioxide just as grape 

 sugar is. Such yeasts are of great importance in the prepara- 

 tion of koumiss and kephir, beverages which have long been made 

 by Mongolian races and those living in the Caucasus. Koumiss 

 is prepared from mare's milk, and kephir from cow's milk. 



The effect of the action of these specific milk sugar-fermenting 

 yeasts along with certain bacteria is to give rise to an alcoholic 

 and also an acid fermentation, whereby lactic acid is formed and 

 the casein undergoes changes which render it more easily 

 assimilable. 



Certain micro-organisms, the so-called lactic acid bacteria, 

 cause milk sugar to be changed into lactic acid according to the 

 following equation : 



C 12 H,A, + H 2 = 4C 3 H,A, 



1 Lo<\ rif. a Ann. de Plmt. Pasteur, Vol. I, 1887. 



