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650 MILK.
fore an action on casein even in the absence of lime-salts. These last
are only necesary for the coagulation or the separation of the curd,
and the process of coagulation is hence a two-phase process. The first
phase is the transformation of the casein by the rennin, the second is
the visible coagulation caused by the lime-salts. This fact, which was
first proved by Hammarsten, was later confirmed by Arthus and Pages
and recently closely studied by Fuld, Spiro, and Laqueur and others.1
The curd formed on the coagulation of milk contains large quantities of
calcium phosphate. According to Soxhlet and Soldner, the soluble lime-salts
are of essential importance only in coagulation, while the calcium phosphate
is without importance. Cocrant believes that the calcium-casein on coagula-
tion may earn’ down with it, if the solution contains dicalcium phosphate, a part
of this as tricalcium phosphate, leaving mono-calcium phosphate in the solution.
A solution of calcium casein is not coagulated by rennin alone but only when soluble
lime-salts are added. Contrary to the generally accepted view that the soluble
lime-salts are of importance in the coagulation, van Dam 2
claims that it is the
quantity of lime combined with the casein which is of importance in the coagula-
tion process. The role of the lime-salts in coagulation is not clear, and this fol-
lows from the chemical procedure in rennin coagulation.
If one makes use of a pure solution of casein and as pure rennin as
possible, then after coagulation it is always found that the filtrate con-
tains very small amounts of a protein, the whey protein, which is probably
formed in the coagulation. This behavior, which was first shown by
Hammarsten, has been substantiated by many others and recently by
Fuld, Spiro and Schmidt-Nielsen. Whey protein is generally con-
sidered as a proteose substance, and Koster 3
found 13.2 per cent nitro-
gen therein. In correspondence with these observations casein coagula-
tion with rennin is considered as a cleavage process, in which the principal
mass of the casein, sometimes more than 90 per cent, is split off as para-
casein* a body closely related to casein, and in the presence of sufficient
1
See Maly’s Jahresber., 2 and 4; also Hammarsten, Zur Kenntniss des Kaseins und
der Wirkung des Labfermentes, Nova Acta Reg. Soc. Scient. Upsala, 1877, Fest-
schrift; Zeitschr. f. physiol. Chem., 22; Arthus et Pages, Arch, de Physiol. (5), 2,
and M6m. soc. biol., 43; Fuld, Hofmeister’s Beitrage, 2, and Ergebnisse der Physiol.,
1, Abt. 1, where a good review of the literature may be found, Spiro, Hofmeister’s
Beitrage, 6 and 7, with Reichel, ibid., 7 and 8; Laqueur, ibid., 7.
2
Zeitschr. f. physiol. Chem., 58.
’Hammarsten, 1. c; Fuld. Bioch. Zeitschr., 4, and Hofmeister’s Beitrage, 10;
Spiro, Hofmeister’s Beitrage, 8; Schmidt-Nielsen, Hammarsten’s Festschrift, 1906;
Koster, see Maly’s Jahresber., 11, 14.
* It has been proposed to designate the ordinary casein as caseinogen and the curd
as casein. Although such a proposition is theoretically correct, it leads in practice
to confusion. On this account the author calls the curd paracasein, according to
Schulze and Rose (Landwirthsch. V’ersuchsstat., 31). A summary of the literature on
the casein coagulation may he found in E. Fuld, Ergebnisse der Physiol., 1; Raudnitz,
ibid.. 2; and Laqueur, Biochem. Centralbl., 4, 344.
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