CHEMISTRY OF DIGESTION AND NUTRITION. 33 J 



Conditions Affecting the Supply of Glycogen in Muscle and Liver. — 

 In accordance with the view given above of the general value of glycogen — 

 namely, that it is a temporary reserve supply of carbohydrate material that 

 may be rapidly converted to sugar and oxidized with the liberation of energy — 

 it is found that the supply of glycogen is greatly affected by conditions calling for 

 increased metabolism in the body. Muscular exercise will quickly exhaust the 

 supply of muscle and liver glycogen, provided it is not renewed by new food. 

 In a starving animal glycogen will finally disappear, except perhaps in traces, 

 but this disappearance will occur much sooner if the animal is made to use its 

 muscles at the same time. It has been shown also by Morat and Dufourt that 

 if a muscle has been made to contract vigorously, it will take up much more 

 sugar from an artificial supply of blood sent through it than a similar muscle 

 which has been resting; on the other hand, it has been found that if the nerve 

 of one leg is cut so as to paralyze the muscles of that side of the body, the amount 

 of glycogen will increase rapidly in these muscles as compared with those of 

 the other leg, that have been contracting meantime and using up their glycogen. 

 Formation of Urea in the Liver. — The nitrogen contained in the proteid 

 material of our food is finally eliminated, after the metabolism of the proteid 

 is completed, mainly in the form of urea. As will be explained in another 

 part of this section, it has been definitively proved that the urea is not formed in 

 the kidneys, the organs that eliminate it. It has long been considered a 

 matter of the greatest importance to ascertain in what organ or tissues urea is 

 formed. Investigations have gone so far as to demonstrate that it arises in part 

 at least in the liver; hence the property of forming urea must be added to the 

 other important functions of the liver-cell. Schroder 1 performed a number of 

 experiments in which the liver was taken from a freshly-killed dog and irri- 

 gated through its blood-vessels by a supply of blood obtained from another 

 dog. If the supply of blood was taken from a fasting animal, then circulating 

 it through the isolated liver was not accompanied by any increase in the amount 

 of urea contained in it. If, on the contrary, the blood was obtained from a 

 well-fed dog, the amount of urea contained in it was distinctly increased by 

 passing it through the liver, thus indicating that the blood of an animal after 

 digestion contains something that the liver can convert to urea. It is to be 

 noted, moreover, that this power is not possessed by all the organs, since 

 blood from well-fed animals showed no increase in urea after being circu- 

 lated through an isolated kidney or muscle. As further proof of the area- 

 forming power of the liver Schroder found that if ammonium carbonate was 

 added to the blood circulating through the liver — to that from the fasting as 

 well as from the well-nourished animal — a very decided increase in Hie urea 

 always followed. It follows from the last experimenl that the liver-cells arc 

 able to convert carbonate of ammonium into urea. The reaction may l»c ex- 

 pressed by the equation (MI, ),('()— 2H a O= CON, II,. SchondorffMn some 

 later work showed that if the Id 1 of a fasting dog is irrigated through 



1 Archiv fur experimentelle Pathologie und Pharmakologie, Bde xv. and xix., L882 and 1885. 



2 Pfliiger'a Archiv fur die gesammtc Pltysioloi/ir, is 1 .):!, |', ( |. 1 i v. S. 1'Jii. 



