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392 THE LIVER.
ammoniacal basic lead acetate. An aqueous solution of glycogen made
alkaline with caustic potash (15 per cent KOH) is completely precipitated
by an equal volume of 96 per cent alcohol. Tannic acid also precipitates
glycogen. It gives a Avhite granular precipitate of benzoyl-glycogen
with benzoyl chloride and caustic soda. Glycogen is completely pre-
cipitated by saturating its solution at ordinary temperatures with magne-
sium or ammonium sulphate. It is not precipitated by sodium chloride,
or by half saturation with ammonium sulphate (Nasse, Neumeister,
Halliburton, Young 1
). On boiling with dilute caustic potash (1-2
per cent) the glycogen may be more or less changed, especially if it has
been previously exposed to the action of acid or to Brucke’s reagent
(see below) (Pfluger). On boiling with stronger caustic potash (even
of 36 per cent) it is not injured (Pfluger). By diastatic enzymes
glycogen is converted into maltose or glucose, depending upon the nature
of the enzyme. It is transformed into glucose by dilute mineral acids.
According to Tebb 2 various dextrins appear as intermediary steps in
the saccharification of glycogen, depending on whether the hydrolysis
is caused by mineral acids or enzymes. The glycogen from various
animals and different organs is the same according to Pfluger.3
Nor has
it been decided whether all the glycogen in the liver occurs as such or
whether it is in part combined with protein (Pfluger-Nerking). The
investigations of Loeschcke 4 have shown that we have no positive
reasons for this assumption.
The preparation of pure glycogen (most easily from the liver) is
generally performed by the method suggested by Brucke, of which the
main points are the following: Immediately after the death of the animal
the liver is thrown into boiling water, then finely divided and boiled
several times with fresh water. The filtered extract is now sufficiently
concentrated, allowed to cool, and the proteins removed by alternately
adding potassium-mercuric iodide and hydrochloric acid. The glycogen
is precipitated from the filtered liquid by the addition of alcohol until
the liquid contains 60 vols, per cent. By repeating this and precipitating
the glycogen several times from its alkaline and acetic-acid solution it
is purified on the filter by washing first with 60 per cent and then with
95 per cent alcohol, then treating with ether, and drying over sulphuric
acid. It is always contaminated with mineral substances. To be able
to extract the glycogen from the liver or, especially, from muscles and
other tissues completely, which is essential in a quantitative estimation,
these parts must first be warmed for two hours with strong caustic potash
(30 per cent) on the water-bath. As the glycogen changes in this purifica-
1
Young, Journ. of Physiol., 22, citing the other investigators.
2
Jonrri. of Phyeiol., 22.
* Pfluger’s, Arch. 129.
* Ibid., 102.
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