692 PHYSIOLOGICAL CHEMISTRY. 



Fecal calculi. Feces sometimes contain hard masses, known as 

 coproliths and enteroliths. Coproliths are inspissated feces. Entero- 

 liths usually consist of concentric layers of earthy phosphates and 

 insoluble soaps around a nucleus of a piece of bone, a fruit-stone, 

 etc. Pancreatic stones consist of calcium phosphate and carbonate 

 without cholesterin or bile-pigment. Intestinal sand is the name 

 given to certain small calculi occurring in the feces. They are com- 

 posed of magnesium and calcium soaps, cholesterin, bile-pigment, 

 salts of magnesium, and some of the hydroxy acids, such as succinic 

 acid. The clinical significance of these concretions is not definitely 

 known. 



The liver. The anatomical relations of the liver indicate the im- 

 portance of this organ in assimilation, digestion, and excretion. The 

 digestive function of the liver, which is comparatively slight, and the 

 excretory function are carried out largely by means of the bile. The 

 digestive properties of bile have been considered. 



While it is probable that the liver has some action on the protein 

 material brought to it by the portal system directly after its digestion 

 and absorption in the intestine, this has not been proved. It is, how- 

 ever, known that the main nitrogenous excretion of the body, the 

 urea of the urine, is formed here, and is merely excreted by the 

 kidneys. The mechanism of this urea production is not clear. It is 

 likely that the waste nitrogen is brought to the liver in the form of 

 ammonium salts (carbonate or carbamate), and by it is transformed 

 into urea. Liver tissue has the power of producing such a change 

 under experimental conditions, but it has not been proved that the 

 process occurs normally in this manner. In birds the main nitrog- 

 enous excretion, uric acid, has also been shown to be formed in the 

 liver. 



Glycogen is one of the most important constituents of the liver, and 

 undoubtedly represents a storage supply of carbohydrate material. It 

 is derived for the most part directly from the carbohydrates of the 

 food which have been split in the intestine, absorbed as dextrose and 

 laevulose, and carried directly to the liver by the portal vein. Here 

 these simple sugars are converted into the more complex glycogen by 

 a process of dehydration. It is probable that some of the simple as 

 well as the conjugate proteins can also form sugar and, hence, gly- 

 cogen. Some of the sugar excreted in diabetes is certainly derived 

 from the proteins. It is not clear, however, that such a change takes 

 place under normal conditions. The question with regard to the fats 

 is in somewhat the same condition. It has been shown that glycogen 



