GLYCOGEN. 441 



ferments capable of changing glycogen into glucose the 

 latter view is the more probable. Analyses of portal 

 and hepatic bloods, made with the view of determining 

 whether more sugar was carried out of the liver during 

 fasting than into it, are conflicting. The main fact, how- 

 ever, remains that somehow this carbohydrate reserve in 

 the liver is steadily carried off to be used elsewhere: and 

 animal glycogen thus answers pretty much to vegetable 

 starch, which, made in the green leaves, is dissolved and 

 carried away by the sap currents to distant and not green 

 parts (as the grains of corn or tubers of a potato, which 

 cannot make starch for themselves) and in them is again 

 laid down in the form of solid starch grains, which are 

 subsequently dissolved and used for the growth of the ger- 

 minating seed or potato. Reasons have already been given, 

 (p. 423) for believing that the carbohydrate leaving the 

 liver is not oxidized in the blood, but first after it has passed 

 out of that into a living tissue. Among these the muscles at 

 least seem to get some, since a fresh muscle always contains 

 glycogen, and even in normal amount when an animal is 

 starved for some time; the muscle-fibres then, so to speak, 

 calling on the balance with their banker (the liver) so long 

 as there is any. When a muscle contracts this glycogen 

 disappears and some glucose appears, but not an amount 

 equivalent to the glycogen used up; so that the working 

 muscle would appear, probably for its repair after each con- 

 traction (see p. 431), to utilize this substance. 



How it is that the glycogen, which is so rapidly con- 

 verted into grape sugar by the liver ferment after death, 

 escapes such rapid conversion during life has not been 

 satisfactorily answered. Two possible reasons readily sug- 

 gest themselves; the liver ferment may be only produced 

 by dying hepatic cells: or the glycogen in the living cell 

 may not exist free, but combined with other portions of the 

 cell substance so as to be protected; while, after death, 

 post-mortem changes may rapidly liberate it in a condition 

 to be acted upon by the ferment. 



Diabetes. The study of this disease throws some light 

 upon the history of glycogen. Two distinct varieties of it 



