310 PHYSIOLOGY CHAP. 



It is therefore necessary to admit that other organs besides 

 the liver are capable of fixing the sugar in the form of glycogen, 

 since we know that an excess of absorbed sugar cannot circu- 

 late in the blood without being eliminated by the kidneys. We 

 know in fact that almost every animal organ contains small quan- 

 tities of glycogen ; particularly so the muscles, as first shown by 

 Bernard for the muscles of the foetus (1859), and later by Xasse 

 (1869) for the muscles of the adult. The percentage glycogen 

 content of adult muscle is much lower than that of the liver, and 

 seems to vary considerably not only in different animals, but also 

 in different muscles of the same animal. According to E. Yoit 

 the glycogen content of the whole of the muscles is slightly in 

 excess of that stored up in the liver. In muscular work, by 

 analogy with what occurs in fasting, the glycogen is consumed 

 until it entirely disappears, not merely from the liver but from 

 the muscles also. According to Klilz and Aldehoff the glycogen 

 of the liver disappears more rapidly than that of the muscles, as if 

 the liver supplied it to the muscles in proportion as they use it up. 

 In muscles paralysed by section of the nerves that supply them, 

 increase of glycogen has been found accumulated in consequence 

 of the muscular immobility. In experimental strychnine tetanus, 

 on the other hand, the glycogen can be made to disappear from 

 the muscles and also from the liver. When the muscles enter into 

 rigor mortis the glycogen is converted into glucose and lactic acid. 



All embryonic tissues, as Bernard already recognised, contain 

 a considerable amount of glycogen (particularly the muscles and 

 the placenta), so long as the liver is little developed, and contains 

 only traces of glycogen. Later on the muscles gradually lose their 

 glycogen, while the liver accumulates more and more of it. 



It is not certain that the glycogen of the muscles is identical 

 with that of the liver. Hepatic glycogen is certainly conveyed to 

 the muscles in the form of glucose, since Kiilz demonstrated that 

 the muscles also are capable of fixing the sugar and converting it 

 into glycogen. In fact, the glycogen content of the muscles can 

 be increased in a frog deprived of its liver, by subcutaneous injec- 

 tion of sugar. On the other hand, the presence of glycogen in 

 the blood plasma has not been demonstrated, and where traces are 

 found, these are due to the disintegrated leucocytes which, like all 

 other tissue-cells, contain glycogen (Frerichs). 



The glycogen of the liver, as also of the muscles, is rapidly 

 consumed when the animal is made to develop much heat to keep 

 its temperature constant. If a rabbit be cooled in a cold bath, or 

 kept in an atmosphere below zero, all the glycogen accumulated 

 in the liver disappears (Klilz). The same occurs with white rats 

 (Zatsch). Cold-blooded animals exhibit the opposite phenomenon. 

 If the temperature is raised, their glycogen disappears, owing to 

 accelerated metabolism. When a hibernating frog, whose cells 



