96 GLYCOGEN. 



muscles 1 , also in white blood- and pus-corpuscles 2 and other contractile 

 protoplasm (Aethalium septicum) 3 , in which its presence is signifi- 

 cantly 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 

 molluscs, as for instance 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 mercury and potassium (Briicke's reagent) 8 , as long 

 as any precipitate is formed. The precipitated proteids are again 

 removed by filtration, the glycogen precipitated by the addition of 

 two volumes of 95 p.c. alcohol 9 , collected on a filter, washed tho- 

 roughly 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 accurate 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 secondarily owing to 

 a possible loss during the precipitation and removal of the proteids with which 



1 Nasse, Pfliiger's Arch. Bd. n. (1869), S. 97. . 



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



3 See refs. on p. 4. Also Kuhne, Physiol. Chem. 1868, S. 334. 



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



5 Bizio, Comp. Rend. T. LXII. (1866), p. 675. 



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

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



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



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

 freshly precipitated iodide of mercury ; on cooling this is filtered and the nitrate 

 employed as directed. 



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



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



