DIGESTION. 125 



UREA AND URIC ACID. 



The liver receives products from the muscles, as ammonium 

 carbonate, and builds it into urea. It also destroys uric acid. 



Jaundice is a discoloration of the skin due to the reabsorption 

 of bile by the lymphatics of the liver. This is usually due to 

 obstruction of the bile-ducts by a catarrh, a calculus, or a tumor. 

 Arsenuretted hydrogen and toluylendiamin will produce jaundice. 



Influence of Drugs on Secretion of Bile. Podophyllin, aloes, 

 nitrohydrochloric acid, ipecacuanha, euonymin, and sodium phos- 

 phate stimulate the bile-secreting apparatus. Other substances, like 

 calomel, stimulate the intestinal glands, but not the liver-cells. The 

 best stimulant of the liver is bile-acids in ox-gall, but it is impor- 

 tant to remember that bile in the intestine is liable to be abvsorbed; 

 hence it is best to combine a purgative with it to carry it down the 

 intestinal canal. 



THE SUCCUS ENTERICUS. 



By most physiologists the presence of a certain liquid product, 

 occurring upon the surface of the intestinal mucous membrane, is 

 attributed to the secretory powers of the crypts of Lieberkiihn and 

 the glands of Brunner, presumably due to their columnar cells, 

 although the real mechanism of its secretion is still unknown. To 

 this secretion the name succus entericus has been commonly given. 

 As described by Thiry, it is "a limpid, opalescent, light-yellow- 

 colored fluid, strongly alkaline in reaction, and possessing a specific 

 gravity of 1.010." It contains proteid and mucin, while its great 

 alkalinity is due to the presence of a considerable quantity of sodium 

 carbonate; the latter's presence is easily detected by the efferves- 

 cence, resulting upon mixture with dilute acids. The amount 

 secreted daily is, perhaps, about two pounds. Erepsin, a ferment 

 found in the succus entericus, does not act on albumins, but breaks 

 up albumoses, peptones, casein, protamin, and histon, changing them 

 into leucin, tyrosin, and ammonia. 



The succus entericus also contains a ferment like that in yeast 

 invertin. This body inverts cane-sugar into dextrose and laBvu- 

 lose, and maltose into two molecules of dextrose. On cane-sugar 

 it acts as follows: 



C 12 H 22 1 + H 2 = C 6 H 12 6 + C 6 + C 6 H 12 



Sucrose. Water. Dextrose. Laevulose. 



This inversion is necessary for the absorption of these sugars. 



All sucklings, including the new-born child, have lactase present 

 in the pancreatic and intestinal juice. Weinland has shown that a 



