LACTOSE. 621 



found in these two kinds of milk, as well as certain others, a proteolytic 

 enzyme which they call galactase, which is allied to trypsin, but differs 

 therefrom in that it develops ammonia from milk even in the early stages 

 of digestion. The occurrence of such an enzyme is denied by ZAITSCHEK 

 and v. SZONTAGH, but on the other hand VANDEVELDE, DE WAELE, and 

 SUGG 1 confirm the occurrence of a proteolytic enzyme in milk. 



Orotic acid, CgHnNaO^HX), is the name given by BISCARO and BELLONI 2 

 to a new constituent of milk which they have discovered. This acid, which can 

 be precipitated by basic lead acetate from whey free from protein, is slightly 

 soluble in water, crystalline, and gives several crystalline salts. The mono- 

 methyl and ethyl esters of this acid are also known. It yields urea on treatment 

 with potassium permanganate. 



Lactose, MILK-SUGAR, C^H^On + H^O. This sugar, on hydrolysis, 

 can be split into two hexoses, dextrose and galactose. It yields mucic acid, 

 besides other organic acids, by the action of dilute nitric acid. Levulinic 

 acid is formed, besides formic acid and humin substances, by the stronger 

 action of acids. By the action of alkalies, among other products we 

 find lactic acid and pyrocatechin. 



Milk-sugar occurs, as a rule, only in milk, but it has also been found 

 in the urine of pregnant women on stagnation of milk, as well as in the 

 urine after partaking of large quantities of the same sugar. 



Lactose, of which, according to TANRET, S there are three modifica- 

 tions, occurs ordinarily as colorless rhombic crystals with 1 molecule of 

 water of crystallization, which is driven off by slowly heating to 100 C., 

 but more easily at 130-140 C. On quickly boiling down a milk-sugar 

 solution, anhydrous milk-sugar separates out. Milk-sugar dissolves 

 in 6 parts cold or in 2.5 parts boiling water; it has a faintly sweetish 

 taste. It does not dissolve in ether or absolute alcohol. Its solutions 

 are dextrogyrate. The rotatory power, which on heating the solution to 

 100 C. becomes constant, is (a) D =+52.5. Milk-sugar combines with 

 bases ; the alkali combinations 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 E. FISCHER 4 found that the milk-sugar is first split into dextrose 

 and galactose by an enzyme, lactase, existing in the yeast. The prep- 

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

 cow's milk is based upon this fact. Other micro-organisms also take 

 part in this change, causing a lactic-acid fermentation of the milk-sugar. 



1 Babcock and Russel, Centralbl. f. Bakt. u. Parisitenkunde (II), 6, and Maly's 

 Jahresber., 31; Zaitschek and v. Szontagh, Pfliiger's Arch., 104; Vandevelde, de 

 Waele, and Sugg, Hofmeister's Beitrage, 5. 



2 See Chem. Centralbl., 1905, 2, 63. 



3 Bull. soc. chim. (3), 13. See also Hudson, Journ. Amer. Chem. Soc., 30. 



4 Ber. d. d. Chem. Gesellsch., 27. 



