470 THE HUMAN BODY. 



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 germinating seed or potato. Eeasons 

 have been given in an early part of this chapter for believing 

 that the carbohydrate leaving the liver is not oxidized in the 

 blood, but only after it has passed out of that into the organ- 

 ized tissue. Among these the muscles at least seem to get 

 some, since a fresh muscle always contains glycogen, and even 

 to retain it in normal amount after an animal has been starved 

 for some time; the muscle-fibres then, so to speak, drawing 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, it is probable, 

 uses this substance, among others, for its repair after each 

 contraction. 



How it is that the glycogen, which is so rapidly converted 

 into grape-sugar by the dying liver, escapes such rapid con- 

 version during life has not been satisfactorily answered. It 

 may be that the metabolisms of the dying hepatic cell include 

 processes which are an exaggeration of those occurring dur- 

 ing normal life; in some such way as the production of myo- 

 sin in dying muscle is apparently an exaggeration of chemical 

 changes occurring in norma^contracting muscle: or the gly- 

 cogen in the living cell may not exist free, but combined 

 with other portions of the cell substance so as to be pro- 

 tected ; while, after death, post-mortem changes may rapidly 

 liberate it in a condition to be acted upon. 



Diabetes. The study of this disease throws some light 

 upon the history of glycogen. Two distinct varieties of it 

 are known; one in which sugar appears in the urine only 

 when the patient takes carbohydrate foods; the other in 

 which it is still excreted when he takes no such foods, and 

 mnst therefore form sugar in his Body from substances not at 

 all chemically allied to it. The more probable source of the 

 sugar in the latter case is proteids; since some glycogen is 

 found in the livers of animals fed 011 proteids only, while fats 

 by themselves give none of it. It seems that the proteid 

 molecule, in some complex way, is split up in the liver into a 

 highly nitrogenized part (urea or an antecedent of urea) and 



