66 LECTURE IV. 



liver cells, the molecules of d-glucose are made to unite together again 

 with loss of water and the formation of a new polysaccharide, glycogen. 

 In making this transformation the animal organism acts precisely like the 

 plant in forming cellulose, the circulating sugar being removed from 

 metabolism, stored up and protected from combustion in such a way 

 that at any given moment it can be made " liquid " again. This stage 

 in the metabolism, of carbohydrates in the animal system can be demon- 

 strated very simply by means of the following experiment: A number 

 of rabbits may be kept from food for a length of time until it is known 

 as a matter of experience that the glycogen content of the organs, espe- 

 cially the liver, has been brought as low as possible. This is the case at 

 the end of about ten days. As we shall see later on, the consumption of 

 glycogen can be accelerated greatly by muscular work (whether by actual 

 body work e.g. dogs running in a tread-mill or by muscular convul- 

 sions produced by strychnine poisoning), and thus the time required for 

 the experiment greatly shortened. A part of the animals experimented 

 upon are then fed with a diet rich in carbohydrates. If now all the 

 animals are killed, those that are starving as well as those which have 

 been recently fed and are in the act of digesting the food, the former, 

 when subjected to quantitative tests, will be found to contain only 

 traces of glycogen in the liver, whereas the latter will contain a large 

 amount. 1 This state of affairs is of regular occurrence, so that to-day 

 there is scarcely any one who doubts that there is a direct connection 

 between the carbohydrates taken up (the absorbed d-glucose) and the 

 glycogen. 2 The fact that the liver actually forms glycogen directly from 

 sugar has been demonstrated recently by Karl Grube. 3 Grube passed blood 

 rich in sugar through the liver of a dog, and could detect a slight increase 

 in the liver-glycogen. It is another question as to whether all carbo- 

 hydrates, for example, the pentoses, are capable of forming glycogen in 

 this way. We shall later on take up this point more in detail, but at this 

 place it is of interest for us to know merely how the more important carbo- 

 hydrates in food, namely, starch, cane-sugar, and grape-sugar, behave in 

 this respect. Starch, as we have already seen, is decomposed eventually 

 into molecules of d-glucose, and the same is true of saccharose. From the 

 latter, however, not only d-glucose but an equal amount of d-fructose is 

 formed, the latter being a ketohexose. The question that now arises is, 



1 Cf. F. W. Pavy: Phil. Transact, for 1860, p. 579, and Researches on the Nature and 

 Treatment of Diabetes, London, 1862. Also The Physiology of Carbohydrates, 1894. 

 See also Pfluger's Das Glycogen und seine Beziehung zur Zuckerkrankheit, and Cremer's 

 Physiologic das Glykogens, Ergeb. Physiol. (Asher u. Spiro) 1, p. 803 (1902.) 



2 Carl Voit has furthermore shown that subcutaneous introduction of d-glucose into 

 rabbits caused an increase of up to eight per cent glycogen in the liver. Z. Biol. 28, 

 245, 288 (1891). See also Erwin Voit: Z. Biol. 25, 551 (1889). 



3 Pfliiger's Arch. 107, 490 (1905). 



