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128 THE PROTEIN SUBSTANCES.
or alkalies, and by the putrefaction of the same. They may also be
formed in very small quantities, as by-products, in the investigations
of animal fluids and tissues, and the question as to the extent to which
these exist preformed under physiological conditions requires very
careful investigation.
Between the peptone, which represents the final cleavage product,
and the proteose, which stands closest to the original protein, we have
undoubtedly a series of intermediate products. Under such circum-
stances it is a difficult problem to try to draw a sharp line between the
peptone and the proteose group, and it is just as difficult to define our
conception of peptones and proteoses in an exact and satisfactory manner.
In the past we used to consider the peptones as the end products
in the hydrolysis, they still being true proteins, but we must call atten-
tion to the fact that since that time we have learned of polypeptide-
like cleavage products of the proteins, and also that polypeptides have
been prepared synthetically. With this in mind it is not possible to
say what we understand by the conception true proteid, and also that
possibly there exists a large number of intermediary steps between the
original modified proteid and the simplest cleavage products. There
is no doubt that those bodies which have been called proteoses and
peptones are chiefly mixtures; and the question has been proposed by
Abderhalden l
whether it is not best to drop the conception of pro-
teoses and to call all products precipitable by ammonium sulphate, etc.,
and previously described as proteoses, peptones.
Although there is much in favor cf such a proposition, still on account
of the great importance which the conception of the proteoses has gen-
erally received, it is probably too early to drop the question of proteoses
entirely from a text-book, and we will therefore, as in the past editions,
discuss the historical development of the proteoses and peptones in
the ordinary sense.
The proteoses (or albumoses) used to be considered as those protein
bodies whose neutral or faintly acid solutions do not coagulate on boil-
ing and which, to distinguish them from peptones, were characterized
chiefly by the following properties: The watery solutions are precipitated
at the ordinary temperature by nitric acid, as well as by acetic acid and
potassium ferrocyanide, and this precipitate has the peculiarity of dis-
appearing on heating and reappearing on cooling. If a proteose solu-
tion is saturated with NaCl in substance, the proteose is partly pre-
cipitated in neutral solutions, but on the addition of acid saturated
with salt it is more completely precipitated. This precipitate, which
dissolves on warming, is a combination of the proteose with the acid.
1
Oppenheirner’s Handb. der Biochern., Bd. 1, 1908.
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