360 STUDIES IN ADVANCED PHYSIOLOGY. 



increased amounts of sugar in the blood would lead to dia- 

 betic results in the kidneys, for it is a commonly observed 

 fact among physicians that an excess of sugars soon reveals 

 itself by a sugary elimination from the kidneys. To avoid 

 both of these dangers all the excess of sugar immediately 

 after a meal is stored in the liver, and observations have 

 been made on the human liver showing that the amount of 

 glycogen so stored may reach 10 per cent, of the weight of 

 that organ. Then during the interval between this meal and 

 the following the liver doles out from time to time this glyco- 

 gen, and so serves to maintain the uniform composition of 

 the blood, adding the glycogen to it as fast as the sugar is 

 used by its tissues. This addition to the blood is, however, 

 not made in the glycogen itself, but this is converted back 

 into dextrose in the liver, and in that form sent into the 

 blood. 



This glycogen may be readily detected. It may be seen 

 microscopically in the liver cells in the form of clear lumps, 

 which when treated with iodine give the chemical test for 

 glycogen. Every chemical student is familiar with the 

 fact that the usual reaction to detect the presence of starch 

 is to treat the same with a solution of iodine. The starch 

 will at once turn a very deep blue. Glycogen, however, 

 does not turn a deep blue, but turns a wine red color, and 

 in this way is easily detected. Unlike starch, too, it is 

 somewhat soluble in water; more readily soluble in hot 

 water, and by this means the glycogen may be readily ex- 

 tracted from minced liver. 



It will be seen, therefore, that the liver is a kind of 

 store-house, keeping a temporary reserve supply of glycogen 

 to be used up in the intervals between meals. It is, to use 

 a common figure, the pocket change to supply the daily 

 needs of the tissue. It is quite interesting to note that the 

 liver is not the only organ in the body which is thus able to 

 take sugar out of the blood and store it up within itself as 

 a reserve supply in the form of glycogen. Glycogen is 

 found in other parts of the body. In white corpuscles, in 



