1882.] On the Structure of the Cells of the Liver. 25 



In winter the amount of fat in the liver varies so much in frogs appar- 

 ently alike, that I do not feel justified in drawing any conclusions as 

 to the changes occurring in digestion. 



The only other vertebrates with liver of the tubular type on which 

 I have made a series of observations, are the toad and newt. The 

 changes in the liver of the toad are in all essential respects the same as 

 those I have described for the liver of the frog. In the newt's liver I 

 have not observed the formation of zones during digestion ; it appears 

 to me to depart largely from the tubular type of gland, and to 

 resemble in structure rather the mammalian than the ordinary 

 amphibian liver. In the snake during the winter's fast, an outer 

 non-granular zone makes its appearance in the liver tubules ; it is, 

 however, much smaller than -that in the frog and toad. 



I may mention that the cells of the frog's bile-duct, where it runs 

 through the pancreas, are ciliated ; the pancreatic duct with con- 

 ciliated cells joins it close to the smalt intestine. 



The Mammalian Liver. 



In the mole the granules of the liver are conspicuous, and are pre- 

 served by osmic acid ; in the dog, cat, and rabbit the granules are 

 more or less altered, hence I have chosen the mole to make observa- 

 tions upon as to the changes which take place in digestion. In the 

 hungry animal the protoplasmic network stretches throughout the 

 cells with nearly equally sized meshes ; in the spaces of the network is 

 a small amount of hyaline substance, partly glycogen, and embedded 

 in this are rather large granules. When the liver is examined six to 

 eight hours after digestion, there is a greater or less disappearance of 

 granules from the centre of the cell around the nucleus ; the network 

 here has wider spaces and thinner bars, and the spaces are for the 

 most part filled with glycogen. In cases where these changes are 

 most marked, osmic acid specimens treated with iodine show a diffuse 

 reddish stained mass surrounding the nucleus ; at the borders of the cell, 

 the yellow stained network is seen, and one or two rows of granules ; 

 between these a little red stained substance may usually be traced 

 continuous with the central mass of glycogen ; the peripheral network 

 and granules make the cell appear at first sight as if it had a very 

 thick cell wall. The network in the central part of the cell is brought 

 out by hardening a piece of the liver in chromic acid and other re- 

 agents. In cells in which the digestive changes are less advanced, 

 the glycogen may only partially surround the nucleus, or may be 

 accumulated more on one side of it than elsewhere. 



Histological observations on the increase of glycogen in the liver- 

 cells have been made by Bock and Hofmann,* on the rabbit, and by 



* Bock u. Hofmann, " Yireliow's Archiv.," 56, s. 201, 1872. 



