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COLLAGENS. 119
somewhat differenl physical properties among each other, hut had about the same
elementary composition, with 0.34 <!.;">:! per cent sulphur. Sadikoff stems to
think that the gelatins prepared up to this time were perhaps not unit bodies
but were possibly mixtures. The bodies prepared by Sadikoff from cartilage
he calls glutting, because they were essentially different from the other gelatins
or glutins. They were poorer in carbon and nitrogen, 17.17 to 17. s7 per cent,
but somewhat richer in sulphur, 0.53-0.718 per cent, than the tendon glutin.
The gluteins differ also from the glutins in thai on boiling with a mineral acid
they have a faint reducing action, and also in that they give a color reaction
with phloroglucin-hydrochloric acid which is probably due to contamination. The
glutins differ from the gluteins by a different behavior with certain salts.
The decomposition products of the collagens are the sum" as those of
the gelatins ami will be found in the table on page 1?5. ( >f special
mention is the fact that gelatin contains no tyrosine and tryptophane
but does yield considerable glycocoll. This latter substance has, because
of its sweet taste, been called gelatin sugar. Skraup l
has obtained on
the hydrolytic cleavage of gelatin a crystalline acid having the formula
C12H25N5O10, which he calls glutinic acid. Gelatin yields considerable
basic nitrogen, according to Hausmann,2
35.83 per cent of the total
nitrogen. It also yields considerable arginine (9.3 per cent), lysine 5-G
per cent, but only little histidine (0.4 per cent). The aromatic group in
g latin is therefore, as directly shown by Fischer and also by Spiro,3
represented by phenylalanine.
Collagen is insoluble in wr
ater, salt solutions, and dilute acids and
alkalies, but it swells up in dilute acids. By continued boiling with
water it is converted into gelatin. Various collagens are converted into
gelatin with varying readiness; the formation of gelatin occurs also
from difficultly soluble collagens by continuous boiling with water.
Collagen is dissolved by the gastric juice and also by the pancreatic
juice ( trypsin solution) when it has previously been treated with acid
or heated with water above 70° C.4
By the action of ferrous sulphate
corrosive sublimate, or tannic acid, collagen shrinks greatly. Collagen
treated by these bodies does not putrefy, and tannic acid is therefore of
great importance in the preparation of leather.
Gelatin or glutin is colorless, amorphous, and transparent in thin
layers. It swells in cold water without dissolving. It dissolves in warm
water, forming a sticky liquid, which solidifies on cooling when sufficiently
concentrated. As Pauli and Rona 5
have shown, various bodies may
have a different influence upon the gelatinization-point of a gelatin
1
Monatshefte f. Chem., 26.
2
Zeitsehr. f. physiol. Chem., 27.
3
Fischer, Levene and Aders, Zeitschr. f. physiol. Chem., 35; Spiro, Hofmeister’s
Beitrafre, 1.
4
Kiihne and Ewald, Verh. d. Xaturhist. Med. Vereins in Heidelberg, 1877, 1.
5 Hofmeister’s Beitrage, 2.
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