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646 MILK.
The observations of Ascherson 1
show that drops of fat, when dropped in an
alkaline protein solution, are covered with a fine albuminous coat, a so-called haptogen-
membrane. As milk on shaking with ether does not give up its fat, or only very
slowly in the presence of a great excess of ether, and as this takes place very readily
after the addition of acids or alkalies, which dissolve proteins, it was formerly
thought that the fat-globules of the milk were enveloped in a protein coat. A
true membrane has not been detected; and since, when no means of dissolving
the protein is resorted to—for example, when the milk is precipitated by carbon
dioxide after the addition of very little acetic acid, or when it is coagulated by
rennet—the fat can be very easily extracted by ether, the theory of a special albu-
minous membrane for the fat-globule has been generally abandoned. The observa-
tions of Quincke 2
on the behavior of the fat-globules in an emulsion prepared
with gum have led, at the present time, to the conclusion that each fat-globule
in the milk is surrounded by a stratum of casein solution held by molecular attrac-
tion, and this prevents the globules from uniting with each other. Everything
that changes the physical condition of the casein in the milk or precipitates it
must necessarily help the solution of the fat in ether, and it is in this way that the
alkalies, acids, and rennet act.
V. Storch has shown, in opposition to these views, that the milk-
globules are surrounded by a membrane of a special slimy substance.
This substance is very insoluble, contains 14.2-14.79 per cent nitrogen,
and yields a sugar, or at least a reducing substance, on boiling with
hydrochloric acid. It is neither casein nor lactalbumin, but it seems to
all appearances to be identical with the so-called " stroma substance
"
detected by Radenhausen and Danilewsky. Storch was able to
show, by staining the fat-globules with certain dyes, that this substance
enveloped them like a membrane. Recently Voltz has given further
proofs of the view that the fat-globules probably have a membrane,
which in his opinion is a very labile formation of variable composition,
and Bauer has also given further proofs for the assumption of a mem-
brane. Droop-Richmond and Bonnema,3
on the other hand, present
several deductions conflicting with Storch’s theory. If Storch’s observa-
tion that the purified fat-globules contain a special protein substance
differing from the dissolved proteins of the milk is correct, then the
assumption as to a special body forming a membrane or stroma of the
fat-globules becomes very probable. The correctness of Storch’s view
has been substantiated very recently by Abderhalden and Voltz.4
On the acid hydrolysis of the fat-globules they obtained glycocoll, which
is absent in the casein as well as in the lactalbumin, and this shows that the
1
Arch. f. Anat. u. Physiol., 1840.
* Pfluger’s Arch., 19.
1
V. Storch, see Maly’s Jahresber., 27; Radenhausen and Danilewsky, Forschungen
auf dem Gebiete der Viehhaltung (Bremen, 1880), Heft 9; Voltz, Pfluger’s Arch., 102;
Bauer, Bioch. Zeitecbf. 32; Droop-Richmond, see Chem. CentralbL, 1094, 2, 356;.
Bonnema, ibid., 1243.
4
Zeitschr. f. physiol. Chem., 59.
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