232 PRODUCTION OF 



stance into glycogen is a dehydration; that is, the separation from it 

 of the elements of water, as follows : 



Glucose. Water. Glycogen. 



C 6 H 12 6 - H 2 = C C H 10 5 . 



It is not possible to say in what manner or by what influence this 

 change takes place ; but it is one of the simplest actions manifested by 

 organic substances, and is known to occur, as well as the opposite change 

 of hydration, in many of the phenomena of both animal and vegetable 

 nutrition. The formation of glycogen from albuminous materials is a 

 more complicated process, and is necessarily accompanied by the appear- 

 ance of another secondary product containing nitrogen ; but we have no 

 certain knowledge as to what this substance may be, or whether there 

 may not be several new compounds formed at the same time. 



Transformation of Glycogen into Sugar. One of the most marked 

 characters of glycogen, as extracted from the liver tissue, is its ready 

 convertibility into glucose by contact with certain organic matters con- 

 tained in the secretions and in the blood. This change takes place 

 partially in the liver itself; and the consequence is that in a state of 

 health the tissue of the organ always contains glucose as well as gly- 

 cogen. In fact, the existence and production of sugar in the liver was 

 a discovery anterior to that of glycogen, having been demonstrated b}' 

 Bernard 1 in 1848. The experiments of this observer, the most important 

 of which have been repeatedly confirmed by others, show that the glu- 

 cose found in the liver of both carnivorous and herbivorous animals has 

 an internal origin, and that it first makes its appearance in the hepatic 

 tissue itself. 



If a dog, cat, or other carnivorous animal, be fed for several days 

 exclusively upon meat and then killed, the liver alone of all the internal 

 organs is found to contain glucose. For this purpose, a portion of the 

 organ should be cut into small pieces, reduced to a pulp by grinding in 

 a mortar with a little water, and the mixture coagulated by boiling with 

 an excess of sodium sulphate. The filtered fluid will then reduce the 

 oxide of copper, with great readiness, on the application of Trommer's 

 test. A decoction of the same tissue, mixed with a little yeast, will 

 also give rise to fermentation, producing alcohol and carbonic acid, as 

 is usual with saccharine solutions. On the contrary, the tissues of 

 the spleen, the kidneys, the lungs, and the muscles, treated in the same 

 way, give no indication of sugar, and do not reduce the salts of copper. 

 Every other organ in the body, as well as the blood of the portal vein 

 by which the liver is supplied, may be destitute of sugar, while the liver 

 always contains it, provided the animal be healthy. 



The presence of sugar in the liver is common to all species of animals, 

 so far as yet known. Bernard found it invariably in monkeys, dogs, 

 cats, rabbits, the horse, the ox, the goat, the sheep, in birds, in reptiles, 



1 Comptes Rendus de 1'Academie des Sciences. Paris, 1850, tome xxxi. p. 571. 



