aiACOdhX J\ I'A'lllolJJGICAL PROCEHHEH 429 



to be detected citliei- 7Hieroseoi)ically oi" clu'inically. Glycogen seems 

 to be formed within tlie cells from the sugar of the blood, through a 

 process of dehydration and polymerization, and to be reconverted 

 whenever necessary into sugar, by a reverse process of hydrolysis. It 

 is quite possible that both of these processes represent merely the 

 reversible action of an intracellular enzyme, but this has not been 

 established. We do know, however, that soon after death the intra- 

 cellular glycogen is rapidly converted into dextrose.-^ 



Properties of Glycogen. — Clycofxen is fieciiu'iitly called an "animal starch," 

 liavinjj the sanio uoiicial composition as tho starches ( r„H,„0,-, ) a?, and apparently, 

 like the starches, it represents a relatively insoluble rcstinfr staf,'e of sufjar in 

 the course of nietaholism. It is readily solulilc in water, formintf an opalescent, 

 colloidal solution, and, therefore, lias no cITect on osmotic pressure, and it is not 

 diffusible. 2C Because of its soluI)ility and the rapidity witli wliicli postmortem 

 <"hange to dextrose occurs, specimens that are to be examined microscopically for 

 glycogen must l)e hardened while very fresh in strontj alcohol, in which srlycojren 

 is insoluble. 2" One of the most characteristic reactions is the port-wine color 

 ^iven by glycofjen when treated with iodin ; this reaction may be applied micro- 

 scopically, solution of the glycogen being avoided by having the iodin dissolved in 

 a solution of gum arable or in glycerol. Salivary ptyalin rapidly converts gly- 

 cogen into glucose, and this reaction may also be used microscopically to prove 

 that suspected granules are glycogen. However, failure to find glycogen micro- 

 chemically does not always mean its absence from a tissue. ^s 



PHYSIOLOGICAL OCCURRENCE 



According to Gierke, the normal glycogen of cells resembles fat 

 in that part of it disappears during starvation, while the rest cannot 

 be removed in this way and probably is something more than a re- 

 serve food-stutf. In distribution glycogen somewhat resembles fat, 

 being abundant in the liver ~^ and muscles, but Gierke considers 

 that the microscopic evidence of the quantity of glycogen present in 

 the cell agrees better with the results of actual chemical analysis than 

 is the case with fat. Rusk,''" however, tinds only a general agreement, 

 wdth marked exceptions. Neither iodin nor Best's carmin stain are 

 absolutely specific for glycogen, but Gierke believes that we may 

 safely consider a substance as glycogen when it is homogeneous, 

 rather easily soluble in water and more so in saliva, gives the usual 

 iodin reaction, and stains bright red with Best's carmin solution. ^^ 

 With these controls, the microscopic findings were found to agree 

 closely with the results of direct chemical analysis, and glycogen was 

 found microscopically visible in muscle, liver, lung, heart, uterus, and 



25 Literature concerning phvsiolo2"\' of glycogen by Pfliiirer. Pfliifrer's Arch., 

 1903 (96), 39S: and Cremer. Frireb.'der Phvsiol.. 1902 (1, Abt. 1), Sn.3. 



26 See Gatin-Oru/ewska, Pfliiger's Arch.. 1904 (10.3), 282. 



27 According to TTelman (Cent. f. inn. ]\fed.. 1902 (2.3), 1017), glycogen may be 

 found in specimens preserved in alcohol as long as fifteen years. 



28Bleibtreu and Kato, Pfliiger's Arch., 1909 (127). 118.' 



29 In the livers of two executed criminals Oarnier (Compt. Pend. Soc. Biol., 

 1906 (60), 12.5) found respectively 4 per cent, and 2.79 per cent, of glycogen. 

 3oUniy. of California Publ., Pathol., 1912 (2), 83. 

 31 Concerning staining methods see Klestadt, Joe. cit. 



