1882.] 



On the Structure of the Cells of the Liver* 



23 



is just that produced when iodine is added to a little purified glycogen 

 on a glass slide, and since it is rapidly dissolved by amylolytic ferment, 

 such as an aqueous or glycerine extract of the parotid of a rabbity 



During the summer months the liver of a hungry frog has granules 

 scattered equally throughout the cell, and there is very little glycogen. 

 During the long winter fast the cells change in appearance ; the 

 granules become more and more confined to the inner part of the cell, 

 and form there a marked inner granular zone. The glycogen increases 

 in amount, and is stored up chiefly in the outer part of the cell, where 

 there are no granules. Osmic acid specimens of glands in this condi- 

 tion show two distinct zones, an inner granular one and an outer, 

 apparently homogeneous, one ; the nucleus lies at the border of the 

 two, or if the outer zone is large lies in it alone. When such a 

 specimen is treated with iodine, all or nearly all of the outer zone 

 stains red-brown ; around the granules also a varying amount of red- 

 brown stained substance is found ; the network of the inner zone, the 

 granules, and' the nucleus stain yellow. In these specimens the 

 network of the outer part of the cell cannot at all, or only very im- 

 perfectly be made out. It is, however, seen in sections of the gland 

 which have been hardened in chromic acid. It is continuous with the 

 network of the inner part of the cell, but has wider spaces, and its 

 bars are finer. 



We know that in the oesophageal glands of the frog and in such 

 gastric glands as have been investigated on the point, the changes 

 which take place in the cells in fasting closely resemble the changes 

 which take place in them during digestion. So here, in the li\er of 

 the frog, the changes which take place when the animal is fed closely 

 resemble those gradually established during the winter fasting 

 period. The extent of the changes occurring in digestion depends 

 greatly upon the state of the liver cells before the animal is fed ; in 

 summer the changes are slight, there is only a slight decrease of 

 granules in the outer part of the cell and a slight increase of glycogen. 

 The changes are much more marked when the cells have to start with 

 a small outer non-granular zone ; in such cases in the 6th to 8th hour 

 of digestion the outer zone is large, and in the 24th to 30th the cells 

 become granular throughout. When a frog which has already a large 

 outer non-granular zone is fed the decrease of granules usually lasts 

 a shorter time, and in the 6th to 8th hour of digestion the granules 

 begin to increase. In other words, the using up and formation of 

 granules go on at different relative rates in different nutritive con- 

 ditions of the body. 



The disappearance of granules and the formation of glycogen which 

 takes place in winter frogs is only partly brought about by the 

 absence of food; it is brought about in part perhaps chiefly by the 

 low temperature. If winter frogs, the liver-cells of which have few 



