THE HISTORY OF GLYCOGEN. 



441 



directly from the food. It seems as if in the summer the frog lives up to its 

 capital of hepatic glycogen, spending it as fast almost as it is made, but that 

 during the winter a quantity is funded to provide for the demands of the 

 late winter and early spring. 



This winter storage of hepatic glycogen in the frog seems closely depen- 

 dent on temperature. If a winter frog, whose liver is presumably more or 

 less loaded with glycogen, be exposed for some time to a temperature of 20 

 or a little higher, the liver will afterward be found to contain little or no 

 glycogen (Fig. 114, B) ; and conversely, if a summer frog be exposed to 

 untimely cold, glycogen, though not in any great quantity, begins to be 

 stored up in the liver. 



376. Before we attempt to discuss further how food and other circum- 



FIG. 114. 



Three Phases of the Hepatic Cells of the Frog. (Langley.) -4, eel Is rich in glycogen. Takenfroma 

 frog during winter. The cells are large and proteid granules are massed around the lumen, the ho- 

 mogeneous outer zones of the cells are largely composed of glycogen, which is present in con- 

 siderable abundance. The outer zones contain numerous fat globules, shown as dark spots ; 

 but, as stated in the text, these fat globules vary much. S, cells poor in glycogen. Taken from a 

 winter frog which had been kept at 22 C. for ten days. The cells contain very little glycogen, and 

 the proteid granules are dispersed throughout the cell. In a summer frog well fed on proteids the 

 cells would present a very similar appearance. C, starved cells. Taken from a summer frog after 

 a long fast. The cells are small and almost free from glycogen. The proteid granules are dis- 

 persed throughout the cell. All the specimens were hardened in 1 per cent, osmic acid, and are 

 drawn to the same, or nearly to the same scale. 



stances thus affect the glycogen in the liver, it will be desirable to take up 

 the matter which we left on one side, viz., the consideration of the histo- 

 logical changes occurring in the hepatic cells under various conditions. It 

 will be convenient to begin with the cells of the more distinctly tubular 

 gland of the frog. 



In a frog which has not been subjected to any special treatment the cell 

 substance of the hepatic cell (cf. Fig. 114, A) will generally be found to 

 contain lodged in itself three kinds of material, the presence of which, if 

 not directly recognizable in the fresh cell, may be demonstrated by the 

 use of various reagents. In the first place, oil globules of variable size 



