566 GLYCOGEN IK HEPATIC CELLS. [BOOK n. 



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 late winter and early spring. 



This winter storage of hepatic glycogen in the frog seems 

 closely dependent on temperature. If a winter frog, whose 

 liver is presumably more or less loaded with glycogen, be ex- 

 posed for some time to a temperature of 20 or a little higher, 

 the liver will afterwards be found to contain little or no glyco- 

 gen, Fig. 106 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. 



360. Before we attempt to discuss further how food and 

 other circumstances thus affect the glycogen in the liver, it 

 will be desirable to consider certain histological changes occur- 

 ring 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 treat- 

 ment the cell-substance of the hepatic cell (cf. Fig. 106 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 and in 

 variable amount are scattered throughout the cell ; sometimes, 

 as we have already said, these are extremely abundant ; but 

 there is otherwise nothing very special about these fat globules 

 in the hepatic cell to demand any discussion concerning them 

 apart from the general discussion on the formation of fat, into 

 which we shall enter later on. 



In the second place, a number of small discrete granules 

 may be seen lodged in the cell-substance. These appear to be 

 of a proteid nature and are generally most abundant on the 

 inner side of the cell near the lumen of the bile passage. The 

 presence of these granules is closely dependent on the activity 

 of the digestive processes. They diminish when digestion is 

 going on and accumulate again afterwards. Putting aside cer- 

 tain details we may say that these granules behave very much 

 like the granules in an albuminous salivary cell, a pancreatic 

 cell or a chief gastric cell ; and we may probably safely con- 

 clude that they, like the granules in these cells, are in some 

 way concerned in the formation of the secretion ; that is, in 

 their case, bile. 



In the third place, the cell contains more especially in its 

 outer parts, nearer the blood vessel, away from the lumen of 

 the bile passage, a variable quantity of material which differs 

 from the ordinary cell-substance in being hyaline and refractive 

 and hence glassy looking, and in staining port-wine red with 



