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654 MILK.
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 *
confirm the occurrence of a proteolytic enzyme in milk.
Orotic acid, C5 HnN,04.2H20, is the name given by Biscaro and Belloni l
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, Ci2H220n+H<20. This sugar, on hydrolysis,
can be split into two hexoses, glucose 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 occurs ordinarily as colorless rhombic crystals with 1 mole-
cule 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 («);>= +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 3 found that the milk-sugar is first split into glucose
and galactose by an enzyme, lactase, existing in the yeast. The prep-
aration of milk-wine, " kumyss," from mare’s milk and " kephir " and
" yoghurt " from cow’s milk is based upon this fact. Other micro-organ-
isms 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; Zaitsrhek and v. Szontagh, Pfliiger’s Arch., 104; Vandevelde, de
Waele, and Sugg, Hofmeister’s Beitrage, 5.
* See Chem. Centralbl., 1905, 2, 63.
* Ber. d. d. Chem. Gesellsch., 27.
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