CHAP, v.] NUTRITION. 417 



decoction contained very little sugar, and that the small quantity 

 which was present did not increase even when the decoction was 

 allowed to stand for some time. The decoction, however, was 

 peculiarly opalescent, indeed milky in appearance; whereas the 

 decoction of a liver which had been allowed to remain exposed to 

 warmth for some time after death, before being boiled, and which 

 accordingly contained a large amount of sugar, was quite clear. 

 On adding saliva, or other amylolytic ferment, to the opalescent, 

 sugarless, or nearly sugarless, decoction and exposing it to a gentle 

 warmth (35 40), the opalescence disappeared ; the fluid became 

 clear, and was then found to contain a considerable quantity of 

 sugar. Here again the explanation was obvious. The opalescence 

 of the decoction of boiled liver is due to the presence of a body 

 which is capable of being converted by the action of a ferment 

 into sugar, and is therefore of the nature of starch. At the 

 moment of death the liver must contain a considerable quantity 

 of this substance, which after death becomes gradually converted 

 into sugar, either through the action of some amylolytic ferment 

 present in the hepatic cells or in the blood of the hepatic vessels 

 or possibly by some special agency. Hence the post-mortem 

 appearance of a continually increasing quantity of sugar. By 

 precipitating the opalescent decoction with alcohol, by boiling the 

 precipitate with alcohol containing potash, whereby the proteid 

 impurities clinging to it were destroyed, and by removing adherent 

 fats by ether, Bernard was able to obtain this sugar-producing or 

 glycogenic substance in a pure state as a white amorphous powder, 

 with a composition of C 6 H 10 O 5 , and therefore evidently a kind of 

 starch. Its most striking differences from ordinary starch were 

 that it gave a deep red and not a blue colour with iodine, and that 

 when dissolved in water it formed a milky fluid. He gave to it the 

 name of glycogen. 



Since Bernard's discovery glycogen has been recognized as a 

 normal constituent, variable in quantity, of hepatic tissue both in 

 vertebrate and invertebrate animals. That it is present in the 

 hepatic cells, and not simply contained in the hepatic blood, is 

 shewn by the fact that it remains in the liver after all blood has 

 been washed out of that organ. It has also been found in muscle, 

 of which indeed it is almost a constant constituent, in the placenta, 

 white corpuscles, testes, brain, and in other parts of the body ; the 

 tissues of the embryo at an early stage, especially before the liver 

 has become functionally active, are particularly rich in it. 



We have some reasons for thinking that there are several 

 varieties of glycogen, and that the glycogen which exists in muscle is 

 not quite identical with that which occurs in the liver. Indeed there 

 seem to be intermediate stages between glycogen and starch or 

 dextrin. The physiological value of these differences has not yet 

 however been clearly determined, and, with this caution, we shall in 

 the discussions which follow, speak of glycogen as a single substance. 



p. 27 



