DISTRIBUTION OF GLYCOGEN IN THE BODY 323 



intestinal tract, lining the ducts of glands, in the brain, in 

 ganglion cells (of gastropods at least), in the ovaries and testes 

 and placenta. 



A more detailed account of its distribution is unnecessary 

 here. An important point to keep in mind is that in the 

 embryo it is much more evenly distributed over the body than 

 in the adult, where it becomes located mainly in the liver and 

 muscles. 



With regard to the seat of ylycogeu formation, we would at 

 first sight assume from a consideration of its distribution in 

 the tissues that this is in the hepatic cells. It is most plentiful 

 here, and feeding starved animals with carbohydrates causes 

 glycogen to be deposited first of all in the liver and only later 

 in the muscles. We would thus explain the presence of glycogen 

 in the muscles by its being carried there by the blood. Against 

 such an hypothesis, however, stands the fact that no glycogen 

 has ever been detected in the blood plasma. There is also 

 much evidence that other cells than those of the liver can form 

 glycogen ; yeast cells form it ; it is present in the tissues 

 of primitive animals which possess no liver ; it is formed in the 

 tissues of liverless frogs when solutions of dextrose are injected 

 subcutaneously (E. Ktilz); it is present in the tissues of the 

 developing chick before any liver cells have become differentiated, 

 whereas it is absent in the unhatched egg. It is probable, 

 therefore, that glycogen is formed in the muscles as well as in 

 the liver ; indeed, Naunyn has stated that the colour reaction of 

 muscle glycogen towards iodine is somewhat different from that 

 of liver glycogen, and Bernard has noticed that in paralysed 

 muscles a form of glycogen accumulates which gives a blue 

 instead of a port- wine colour with iodine. 



Attempts have been made to decide this important question 

 i.e. whether tissues other than the liver can form glycogen 

 by perfusing the muscles of one of the hind limbs of a dog with 

 blood containing dextrose, and comparing the glycogen contents 

 of the perfused muscles with those of the other hind limb- 

 Constant results, on which any definite conclusion could be based, 

 have not, however, been obtained. 



It is therefore probable, although absolute proof of the fact 

 is wanting, that glycogen can be independently formed in the 

 liver and other tissues in which it is found. 



