PHYSIOLOGICAL OCCURRENCE OF GLYCOOEN 359 



PHYSIOLOGICAL OCCURRENCE 



According to Gierke, 1 the Dormal 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 reserve food-stuff. In distribution glycogen somewhat 

 resembles fat, being abundant in the liver 2 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. 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. 3 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 

 skin (but not in the brain, where it may be demonstrated chemi- 

 cally in minute quantities). 



Glycogen is especially abundant in fetal tissues, but it is not 

 present in all fetal cells, nor is it always most abundant in the 

 most rapidly growing tissues. Although both fat and glycogen 

 are quite abundant in fetal muscle and liver tissues, the liver of 

 early embryos does not contain either. 4 In extra-uterine life 

 glycogen is relatively less abundant ; invertebrates and the 

 lower vertebrates have more than the higher forms. In mam- 

 malian adults the liver and muscle contain the most glycogen, 

 cartilage standing next, and it is also present in squamous 

 epithelium (particularly the middle layers), but not in slightly 

 stratified (cornea), transitional, or cylindrical epithelium. The 

 normal lung is microscopically glycogen-free (except for its 

 cartilage and muscle), as also are the nervous system, pancreas, 

 salivary glands, thyroid, hypophysis, bone-marrow, and adrenals ; 

 normal human kidneys do not seem to show glycogen, but it 

 may be present in the kidneys of mice, rabbits, and cats. 



1 K complete summary of all the literature to the end of 1904 is given in 

 Gierke's article in Ziegler's Beitr., 1905 (37), 502; hence references included 

 by Gierke will not generally be given. 



2 In the livers of two executed criminals Gamier (Compt. Rend. Soc. BioL, 

 1906 (60), 125) found respectively 4 per cent, and 2.79 per cent, of glycogen. 



3 A special staining method is recommended by Driessen, Cent. f. Path., 

 1905 (16), 129. 



* Adamoff (Zeit. f. BioL, 1905 (46), 288) contests the idea that the amount 

 of glycogen is in direct relation to growth energy. 



