96 GLYCOGEN. 



adult body, as for instance the muscles, 1 also in white blood- and 

 pus-corpuscles 2 and other contractile protoplasm (Aethalium sep- 

 ticum), 3 in which its presence is significantly connected with their 

 specialised activity, not as an essential, as some have supposed, 

 but as a convenient accessory. It is also conspicuously found in 

 the tissues of the embryo before the liver is functionally active, 4 

 and is present in large quantities in many rnollusks, as for in- 

 stance the common oyster 5 (9'5 p.c.). 



It is at present uncertain whether the glycogen obtainable from 

 muscles is identical with that of the liver. It is stated that muscle- 

 glycogen yields a distinctly more purple colour with iodine than does 

 liver glycogen, 6 but their identity is still an. open question. 7 



Preparation of glycogen. The liver of an animal (rabbit or 

 dog), previously fed with copious meals of carbohydrate, is excised 

 as rapidly as possible, cut into small pieces, and thrown into an 

 excess of boiling water, at least 400 c.c. to each 100 gr. of liver. 

 After being boiled for a short time, the pieces are removed, ground 

 up as finely as possible in a mortar with sand or powdered glass, 

 returned to the original water, and boiled again for some time. On 

 faintly acidulating the boiling mass with acetic acid a large amount 

 of the proteid matter in solution is coagulated and may be removed 

 by filtration. The filtrate is now rapidly cooled, and the proteids 

 finally and completely precipitated by the alternating addition of 

 hydrochloric acid and of a solution of the double iodide of mer- 

 cury and potassium (Briicke's reagent), 8 as long as any precipi- 

 tate is formed. The precipitated proteids are again removed by 

 filtration, the glycogen precipitated by the addition of two vol- 

 umes of 95 p.c. alcohol, 9 collected on a filter, washed thoroughly 

 with 60 p.c. spirit, and finally with absolute alcohol and ether 

 (Briicke). 10 



The above method suffices in cases where there is much glycogen 

 present and no quantitative result is desired ; as a matter of fact 

 there is a not inconsiderable loss during its application. The ac- 

 curate determination of glycogen in tissues is a matter of some 

 difficulty, primarily because it is not easy to ensure the complete 

 separation into solution of the glycogen from the tissue, and sec- 



1 Nasse, Pfluger's Arch. Bd. ii. (1869), S. 97. 



2 Hoppe-Seyler, Med.-chem. Unters. Hft. 4 (1871), S. 486. 



8 See refs. on p. 4. Also Kiihne, Physiol. Chem. 1868, S. 334. 

 4 See Preyer's Speeialle Physiol. d. Embryo, Leipzig, 1885, S. 271. 

 * Bizio, Compt. Rend. T. LX'TI. (1866), p. 675. 



6 Naunyn, Arch. f. exp. Path. u. Pharm. Bd. in. (1875), S. 97. Boehm n. 

 Hoffmann, Ibid. Bd. x. (1878), S. 12. Nasse, Pfluger's Arch. Bd. xiv. (1877), S. 479. 



7 See also Musculus u. v. Mering, Zt.f. physiol. Chem. Bd. n. (1878), S. 417. 



8 Prepared by saturating a boiling 10 p.c. soluti of potassium iodide with 

 freshly precipitated iodide of mercury ; on cooling, th. is filtered and the filtrate 

 employed as directed. 



" So that the mixture contains 60 p.c. of alcohol. 

 1 Sitzb. d. Wien. Akad. Bd. LXIII. (1871), 2 Abth. Feb.-Hft., S. 214. 



