188 PHYSIOLOGICAL CHEMISTRY 



glycogen free, and then to feed the substance to be investigated. 

 The animal then may be killed and the glycogen content of liver 

 and muscles estimated. If glycogen is present in quantity it 

 either will have been formed from the material fed, or indirectly, 

 if this food has ' ' spared ' ' or been burned in place of some other 

 glycogen former. A second method is to render the animal dia- 

 betic by puncture, phloridzin or other means. A substance then 

 may be fed, and the amount of sugar in the urine estimated. An 

 increase will indicate that the substance fed is a glycogen or 

 rather glucose former, provided the possible origin of the excess 

 glucose from body constituents is excluded. To render an animal 

 glycogen free, it may be made to fast for some time, to do work, 

 it may be subjected to cold, or thrown into convulsions by giving 

 strychnine. A combination of methods usually gives more satis- 

 factory results than any single method. A method of study de- 

 pending upon quite different technique may be used. The liver 

 may be excised, and kept supplied wjth a circulating medium, 

 either blood or some other fluid. The substance to be studied 

 then may be introduced into the circulating fluid, and the gly- 

 cogen content of the liver later determined. 



It has been found, as might be expected, that glucose forms 

 glycogen. Any substance which will form glucose in the body, 

 thus also will be a possible glycogen former. Fructose, also, 

 and to some extent galactose form glycogen. On hydrolysis, this 

 glycogen is converted into glucose and not into the sugar from 

 which it was produced. This is an interesting fact, as it is an 

 example of a conversion of one monosaccharide into another in 

 the body. Naturally all carbohydrates which are digested to 

 monosaccharides in the alimentary tract thus will be sources of 

 glycogen. It has been shown, however, that there are sources of 

 glycogen other than the carbohydrates. 



If an animal is made diabetic by removal of the pancreas or 

 in some other way, glucose appears in the urine. It continues to 

 be excreted when the glycogen supplies of the body have been 

 exhausted. If protein is fed to such an animal, the amount of 

 glucose in the urine increases. There is a certain parallelism 



