MILK. 307 



gum, and vegetable mucus. By the action of sodium amalgam on 

 milk-sugar we obtain dulcite, mannite, lactic acid, and other pro- 

 ducts. By the action of alkalies we obtain lactic acid among other 

 products. 



Milk-sugar occurs in all milks. It has also been found in the 

 urine of pregnant women. According to BOUCHARDAT, it also 

 occurs in the ripe fruit of the achras sapota. 



Milk-sugar occurs ordinarily as colorless rhombic crystals with 

 1 mol. of water of crystallization, which is driven off by slowly heat- 

 ing to 100 C., but more easily at 130-140 C. At 170 to 180 C. 

 it is converted into a brown amorphous mass, lactocaramel, C 6 H 10 5 . 

 Milk-sugar dissolves in 6 parts cold and in 2.5 parts boiling water; 

 it has a faint sweetish taste. It does not dissolve in ether or abso- 

 lute alcohol. Its solutions are dextro-gyrate. The rotary power, 

 which, on heating the solution to 100 C. becomes constant, is a (D) 

 = -\- 52.5. Milk-sugar combines with bases ; the alkali combina- 

 tions are insoluble in alcohol. 



Milk-sugar is not fermentable with pure yeast. It undergoes, 

 on the contrary, alcoholic fermentation by the action of certain 

 schizomycetes, and lactic acid is then produced thereby. The prep- 

 aration of milk-wine, " kumyss," from mare's milk and "kephir" 

 from cow's milk is based upon this fact. Micro-organisms pro- 

 duce a lactic fermentation in lactose, and this explains the ordinary 

 souring of milk. 



Lactose responds to the reactions of grape-sugar, such as 

 MOORE'S or TROMMER'S and the bismuth test, which will all be 

 described in Chapter XIV on the urine. It also reduces mercuric 

 oxide in alkaline solutions. After warming with phenylhydrazin 

 acetate it gives on cooling a yellow crystalline precipitate of phenyl- 

 lactosazon, C^H^N^Og (see Chap. XIV on sugar in the urine). 

 It differs from cane-sugar by giving positive reactions with 

 MOORE'S and the bismuth test, and also that it does not darken 

 when heated with anhydrous oxalic acid to 100 C. It differs from 

 grape-sugar and maltose by its solubility and crystalline form ; but 

 especially by its not fermenting with yeast and by yielding mucic 

 acid with nitric acid. 



For the preparation of milk-sugar we make use of the by-product 

 in the preparation of cheese, the sweet whey. The albumin is re- 



