CHEMICAL BASIS OF THE ANIMAL BODY. 97 



it is always largely contaminated. The first difficulty may be largely overcome 

 by the addition of caustic potash which dissolves the tissue fragments and thus 

 liberates the glycogen, also by extraction in a Papin's digester 1 in which case the 

 solution is again very complete 2 . 



Glycogen is, when pure, an amorphous white powder, readily 

 soluble in water with which it yields a solution which is usually, but 

 not always, opalescent. This solution contains no particles which are 

 visible under the microscope and niters readily without diminution of 

 the opalescence; the latter may be largely removed by the addition 

 of free alkalis or acetic acid. Under ordinary conditions it is readily 

 precipitated by alcohol when the mixture contains 60 p.c. of the 

 precipitant, but if pure, and in 0*5 I'O p.c. solution, even an excess 

 of absolute alcohol is stated not to cause its precipitation. The 

 precipitation takes place at once on the addition of a trace of sodium 

 chloride 3 . 



It gives a characteristic port-wine colouration with iodine which 

 does not however distinguish it from erythrodextrin since in both 

 cases the colour, contrary to the older and current statements, dis- 

 appears on warming and returns on cooling. On the other hand 

 dextrins are not precipitated by 60 p.c. alcohol, even the most in- 

 soluble of these substances requiring at least 85 p.c. of alcohol for 

 their precipitation, and usually more. It appears that the reaction 

 with iodine is most delicate in presence of sodium chloride 4 . 



Aqueous solutions of glycogen are strongly dextrorotatory, but the 

 statements as to its specific rotatory power must be received with 

 caution. [Boehm and Hoffmann 5 (a) D = + 226 -7. Killz* in '6 p.c. 

 solution (a) D = + 203-5 to +225-6. Landwehr 7 (a) D = + 213-3]. 



The molecular magnitude of glycogen, like that of starch, is unknown. Glycogen 

 yields precipitates with tannic acid, also with calcium and barium hydrate 8 , and 

 with basic lead acetate. No reliance can however be placed on the determination 

 of the molecular weight of glycogen from an analysis of these compounds. 



The hydrolytic products obtained by the action of enzymes and 

 dilute boiling acids on glycogen have not been as fully studied as they 

 have in the case of starch, but the general course of the decomposition 



1 Boehm, Pfluger's Arch. Bd. xxm. (1880), S. 44. 



2 The whole subject is very fully treated by Kiilz in Zt . /. Biol. Bd. xxn. (1886), 

 S. 161, where also the literature is comprehensively quoted. See additionally 

 Nasse, Pfluger's Arch. Bd. xxxvu. (1885), S. 582, and Landwehr, Ibid, xxxvm. S. 321. 

 Panormow (Polish). See Abst. Maly's Jahresb. 1887, S. 304. Cramer, Zt. f. Biol. 

 Bd. xxiv. (1888), S. 67. 



3 Kiilz, Ber. d. d. chem. Gesell Jahrg. 1882, S. 1300. 



4 Nasse, Pfluger's Arch. Bd. xxxvu. (1885), S. 585. 



5 Arch. f. exp. Path. u. Pharm. Bd. vn. (1877), S. 489. 



6 Pfliiger's Arch. Bd. xxiv. (1881), S. 85. 



7 Zt.f.physiol. Chem. Bd. vm. (1883), S. 170. 



8 Nasse, Pfluger's Arch. Bd. xxxvu. (1885), S. 582. 



F. a 



