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652 MILK.
cleins diminishes as the pepsin-hydrochloric acid increases. In the
presence of 500 grams of pepsin-hydrochloric acid to 1 gram of casein,
Salkowski digested the latter completely without obtaining any
pseudonuclein.
In peptic as well as tryptic digestion a part of the organic phosphorus
is split off as orthophosphoric acid, the quantity increasing as the" diges-
tion progresses. Another part of the phosphorus is retained in organic
combination in the proteoses as well as in the true peptones (Salkowski,
Biffi, Alexander, Aders-Plimmer and Bayliss ’).
From the products of peptic digestion of casein, after the separation of the
pseudonuclein, Salkowski 2
has isolated an acid rich in phosphorus. He con-
siders this a paranucleic acid. This acid which gives the biuret test and a
faint xanthoproteic reaction, contains 4.05-4.31 per cent phosphorus. A still
richer product in phosphorus, with 6.9 per cent P, has been isolated by Reh
from the peptic digestive products of casein. He calls this body polypeptid
phosphoric acid. This product, which also gives the above-mentioned protein re-
actions, and is not comparable with the nucleic acids, is characterized by a remark-
ably high content of amino-nitrogen, namely, 23. S per cent. Among the products
obtained by Reh, Dietrich 3
found a mixture of at least four different lime-salts
of a peptone character, and which he considers as polypeptide-like combination
with P2 5 , caseonphosphoric acids. The amount of phosphorus was, respectively,
10.0, 4.1, 3.84 and 3.88 per cent.
Casein may be prepared in the following way: The milk is diluted
with 4 vols, of water and the mixture treated with acetic acid to 0.75-
1 p. m. Casein thus obtained is purified by repeatedly dissolving in water
with the aid of the smallest quantity of alkali possible, by filtering and
reprecipitating with acetic acid and thoroughly washing with water.
Most of the milk-fat is retained by the filter on the first filtration, and the
casein contaminated with traces of fat is purified by treating with alcohol
and ether.
Lactoglobulin was obtained by Sebelien from cow’s milk by saturating
it with NaCl in substance (which precipitated the casein) and saturating
the filtrate with magnesium sulphate. As far as it has been investigated
it had the properties of serglobulin; the globulin isolated by Tiemann 4
from colostrum had, nevertheless, a markedly low content of carbon,
namely, 49.83 per cent.
Lactalbumin was first prepared in a pure state from milk by Sebelien.
He gives its composition as, C 52.19, H 7.18, N 15.77, S 1.73, O 23.13
per cent. Lactalbumin has the properties of the albumins, and Wich-
1
Salkowski, 1. c; Biffi, Virchow’s Arch., 152; Alexander, Zeitschr. f. physiol.
Chem., 25; Plimmer and Bayliss, Journ. of Physiol., 33; See also Kuttner, Pfluger’a
Arch. 129.
2
Zeitschr. f.. physiol. Chem., 32.
1
Reh. Hofmeister’s Beitrage 11; Dietrich, Bioch. Zeitschr. 22.
4
Zeitschr. f. physiol. Chem., 25.
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