22 



Mr. J. N. Langley. 



[Apr. 27, 



mammals is an anastomosing tubular gland. Hence we should 

 expect that the changes which take place during digestion in the liver 

 of an amphibian, reptile, fish, or bird should differ somewhat from 

 those which take place during digestion in the liver of a mammal. I 

 have taken the liver of the frog and toad as an example of the tubular 

 gland form, and have made observations on this during the last two 

 years and a half. How nearly the changes which take place in other 

 "tubular" livers resemble those which take place in the "tubular" 

 livers of the frog and toad can of course only be decided by direct 

 observation ; but it seems unlikely that the change should take any 

 very different course, since the resting state of the cells and their 

 arrangement in the gland is so very nearly the same. 



The Liver of the Frog- 



The liver of the frog and that of the newt can be observed while 

 the blood continues to circulate through it ; in this state nothing is 

 seen in the cells except the fat globules ; if a small piece be teased 

 out in salt solution, the faintly outlined granules are seen floating in 

 the fluid ; these become obvious on adding iodine. The best method 

 for bringing out the granules and fat globules is to place a small piece 

 of the liver in osmic acid, 1 per cent., for a day, to transfer it to alcohol 

 for several days, and then to prepare sections ; in such sections the 

 granules and globules appear to be imbedded in homogeneous cell 

 substance. The granules are largest in the liver of the newt, so that 

 the liver of this animal is best adapted to show that the granules are 

 not the nodal points of the network. The network of the cell is 

 brought out most distinctly by chromic acid, 0~5 per cent. ; it can also 

 be seen in specimens hardened in picric acid, alcohol, mercuric 

 chloride, or in teased out specimens of a liver which has been treated 

 with neutral ammonium chromate r 5 per cent. 



When a section of the liver which contains glycogen, and which 

 has been hardened in acohol or osmic acid, is placed for some minutes 

 in iodine solution, certain parts of the interfibrillar substance of the 

 liver-cells stain red-brown. The substance which is so stained I 

 conclude to be glycogen. By water,, even at 30° C, it is only slowly 

 dissolved. Since isolated glycogen is readily soluble in water, this 

 might lead us to think that the red-staining substance is not glycogen ; 

 but we know that glycogen is not readily extracted from the liver 

 by warm water, and hence it seems probable that a large part of the 

 glycogen of the liver exists in it in a form not very soluble in water ; 

 but, whatever may be the condition of glycogen in the liver, I think I 

 am justified in concluding that the red-staining substance in alcohol 

 specimens is glycogen, since glycogen can be extracted from them, 

 since the amount of the red-staining substance varies directly with 

 the amount of glycogen which can be extracted, since the coloration 



