886 APPENDIX. 



best known are those described by Briicke l under the name of erythrodextrin and 

 achrob'dextrin, the former giving a red color with iodine, the latter not yielding any 

 color at all. Erythrodextrin may be readily converted into a sugar by the action of 

 ferments, and thus is not found as a product of the complete action of ptyalin on 

 starch. Achropdextrin, on the other hand, is not thus converted by ferments, and 

 therefore remains in solution, together with the sugar formed by the action of 

 ptyalin on starch. Achroodextrin may be converted into dextrose by boiling with 

 dilute hydrochloric acid. 



6. Glycogen. C 6 H 10 5 . 



Belongs to the starch division of carbohydrates. Discovered by Bernard in the 

 liver and other organs (see p. 437). 



Glycogen is, when pure, an amorphous powder, colorless and tasteless, readily 

 soluble in water, insoluble in alcohol and ether. Its aqueous solution is generally, 

 though not always, strongly opalescent, but contains no particles visible microscopi- 

 cally ; the opalescence is much reduced by the presence of free alkalies. The same 

 solution possesses, according to Hoppe-Seyler, a very strong dextro-rotatory power, 

 about three times as great as that of dextrose ; 2 it dissolves hydrated cupric oxide ; 

 but this is not reduced on boiling. 



By the action of dilute mineral acids (except nitric) it is partially converted into 

 a form of sugar very closely resembling, though probably differing somewhat from, 

 true dextrose, and the same conversion is also readily effected by the action of amy- 

 lolytic ferments. The sugar into which the glycogen of the liver is naturally con- 

 verted after death (see p. 438) appears to be true dextrose; 3 so also the sugar of 

 diabetes. The result of the action of diastase, or salivary or pancreatic ferment, 

 upon glycogen is, however, according to Musculus and v. Mering,* a mixture of 

 achroodextrin and maltose ; the quantity of dextrose making its appearance at the 

 same time being very small. 



Opalescent solutions of glycogen usually become clear on the addition of caustic 

 alkali; Vintschgau and Dietl 5 have shown that this is accompanied on boiling by 

 a change which converts a portion of the glycogen into a substance to which they 

 gave the name of /3-glycogen- dextrin. (Kuhne 6 had previously described a body 

 to which he gave the name glycogen-dextrin. That described by Vintschgau and 

 Dietl differs slightly from Kuhne' s body, hence the name. According to these 

 authors one-fifth of the glycogen is at the same time changed into some other, at 

 present undetermined, substance. Normal lead acetate gives a cloudiness, the basic 

 salt a precipitate, in solutions of glycogen. 



As tests for this body may be used the formation of a port-wine color with 

 iodine ; this disappears on warming, but returns on cooling. The same color is 

 produced by the action of iodine on dextrin, but this does not reappear on cooling 

 after its disappearance by warming. 



Preparation of glycogen. The following is Brii eke' s 7 method : The filtered or 

 simply strained decoction of perfectly fresh liver or other glycogenic tissue is, when 

 cold, treated alternately with dilute hydrochloric acid and a solution of the 

 double iodide of potassium and mercury 8 as long as any precipitate occurs. In 

 the presence of free hydrochloric acid the double iodide precipitates proteid mat- 

 ters so completely as to render their separation by filtration easy. The proteids 

 being thus got rid of, the glycogen is precipitated from the filtrate by adding 

 alcohol to the extent of between 60 and 70 per cent. Too much alcohol is to be 

 avoided, since other substances as well as glycogen are thereby precipitated. The 

 glycogen is now washed with alcohol, first of 60 and then of 95 per cent. , after- 

 ward with ether, and finally with absolute alcohol. It is then dried over sulphuric 

 acid. 



i Sitzber. d. Wien. Akad., 1872, iii. Abth. Also, Vorlesungen, 2 Aufl., 1875, Bd. i., S. 224. 



2 See Kulz, Pfliiger's Arch., Bd. xxiv. (1881), S. 85. 



3 Pniiger's Arch., Bd. xix. (1879), S. 106, and xxii. (1880), S. 206. Also, Kulz, Ibid., Bd. xxiv. 

 (1881), S. 52. 



^Zeitschr. f. physiol. Chem., Bd. ii. (1878), S. 403. 



5 Pfluger's Arch'., Bd. xvii. (1878), S. 154. 



SLehrb. d. physiol. Chem. (1868). S. 63. 



* Sitzungsber. d. Wiener Akad., Bd. Ixiii. (1871), ii. Abth. 



8 This may be prepared by precipitating potassic iodide with mercuric chloride and dissolving 1 

 the washed precipitate in a hot solution of potassic iodide as long as it continues to be taken up. 

 On cooling, some amount of precipitate occurs, which must be filtered off; the nitrate is then 

 ready for use. 



