PHYSIOLOGY OF THE LIVER AND SPLEEN. 737 



except perhaps in traces, but this disappearance occurs 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 takes 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 is greater in these muscles than in 

 those of the other leg that have been contracting meantime and using 

 up their glycogen. The further history of glycogen is considered in 

 the section on nutrition. 



Formation of Urea in the Liver. The nitrogen contained in 

 the proteid material of our food is finally eliminated, after the metab- 

 olism of the proteid is completed, mainly in the form of urea. 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* performed a number of experiments in which the liver was 

 taken from a freshly killed dog and irrigated through its blood- 

 vessels with 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 followed 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 circulated through an 

 isolated kidney or muscle. As further proof of the urea-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 the urea was always obtained. It follows from the last 

 experiment that the liver cells are able to convert carbonate of 

 ammonium into urea. The reaction may be expressed by the equa- 

 tion (NH 4 ) 2 C0 3 2H 2 = CON 2 H 4 . Schondorff f in some later work 

 showed that if the blood of a fasting dog is irrigated through the hind 

 legs of a well-nourished animal, no increase in urea in the blood can 



* "Archiv f. experimentelle Pathologie und Pharmakologie, " 15, 364, 

 1882, and 19, 373, 1885. 



t " Pfliiger's Archiv f. die gesammte Physiologie, " 54, 420, 1893. 

 47 



