GLYCOGEN AND GLUCOSE IN THE LIVER. 229 



which dissolves the albuminous matters, but does not affect the gly- 

 cogen. After being separated by filtration it is again dissolved in 

 water, the traces of alkali removed by the addition of a little acetic 

 acid, and the glycogen then precipitated anew, in a pure form, by 

 alcohol in excess. It is then dried and may be kept in the form of a 

 white pulverulent mass, which retains its properties for an indefinite 

 time. 



Glycogen thus prepared is soluble in water, its solution having an 

 opalescent tinge. Treated with iodine, it gives a violet color, inter- 

 mediate between the blue reaction of starch and the red of dextrine. 

 It does not reduce the copper salts in Trommer's test, nor give rise to 

 fermentation with yeast ; but it is converted into dextrine and glucose 

 by all those agencies which have a similar effect upon starch namely, 

 prolonged boiling with dilute mineral acids, the contact of vegetable 

 diastase, of saliva, the pancreatic juice, and the serum of blood at a 

 moderately warm temperature. If allowed to remain in the liver after 

 death, a part of it suffers transformation into glucose by contact with 

 the fluids of the hepatic tissue. 



Origin and Mode of Formation of Glycogen. As this substance is 

 present in the liver tissue of both carnivorous and herbivorous animals, 

 it may be derived from the materials of either kind of food. In the 

 carnivora, at least, there is evidence that it is supplied from nitrogenous 

 materials, by the nutritive changes which they undergo in the substance 

 of the liver. Under some circumstances a material resembling glycogen, 

 or identical with it, may be present in the muscles of the herbivora. 

 Bernard has found it in the muscular tissue in rabbits, and especially in 

 pigeons, when fed upon the cereal grains, and in horses kept upon oats 

 and barley; but in all these animals it disappears when the food is 

 changed, or after some days' fasting. Lnchsinger 1 has also found it to 

 be absent from the muscles of the rabbit after several days' fasting, but 

 to continue more persistently in the pectoral muscles of the fowl under 

 similar conditions. 



It is accordingly not a constant but only an occasional ingredient of 

 muscular flesh, and when present is usually found in very small quan- 

 tity. Poggiale, 2 in very many experiments instituted for this purpose 

 by a Commission of the French Academy of Sciences, found glycogen 

 present in ordinary butcher's meat only once. We have also found it 

 to be absent from the fresh meat of the bullock's heart, when examined 

 in the manner described above. Nevertheless, in dogs fed exclusively 

 for eight clays upon this food, glycogen may be abundant in the liver, 

 while it does not exist in the other internal organs, as the spleen, lungs, 

 and kidneys. 



The production of glycogen from nitrogenous substances is also 

 shown, according to Bernard, by the fact that it makes its appearance 



1 Archiv fur die Gesammte Physiologie, 1873. Band viii. p. 290. 



2 Journal de la Physiologie. Paris, 1858, p. 558. 



