454 TEXT-BOOK OF PHYSIOLOGY. 



liver of an animal recently living is removed from the body and its vessels 

 perfused continuously with blood (the urea content of which is known) 

 containing the ammonium salts. An analysis of this blood shows, after a 

 time, a diminution of these salts, and a large increase in the amount of the 

 urea. After the establishment of an Eck fistula (the union of the portal 

 vein with the ascending vena cava whereby the liver is largely excluded from 

 acting on products absorbed from the intestines) there is a marked diminu- 

 tion in the production of urea while the ammonia content of the urine 

 largely increases. One large source for the ammonium which is trans- 

 formed into urea by the liver-cells, is the amino-acid compounds in the in- 

 testine which are not needed for the reconstruction of the protein molecule. 

 These compounds are absorbed by the epithelial cells of the villi and 

 mucous membrane generally, deamidized or deprived of their amino-acid 

 nitrogen (NH 2 ) which is at once converted into ammonia. The ammonia 

 in turn combines with carbon dioxid with formation of ammonium 

 carbonate. When this compound is transported to the liver by the portal 

 blood, the cells convert it into urea in a manner shown in the following 

 formula : 



(NH 4 ) 2 CO 3 - 2H 2 O = CON 2 H 4 . 



Destructive diseases of the liver e.g., acute yellow atrophy, suppuration, 

 cirrhosis largely diminish the production of urea, but increase the quanti- 

 ties of the ammonium salts in the urine. The same is true when the liver 

 cells are destroyed during acute phosphorus poisoning. 



The Conjugation of Products of Protein Putrefaction. One of the 

 important functions of the liver is the conversion of toxic compounds, the 

 products of the putrefaction of proteins, into non-toxic compounds. These 

 compounds are formed in the intestine, are absorbed and carried by the blood 

 of the portal vein to the liver. In their passage through the capillaries of 

 the liver they are conjugated for the most part with potassium sulphate by 

 the action of the liver cells and thus deprived of their toxicity. Among the 

 substances thus conjugated are indol, skatol, phenol, and cresol. After 

 absorption indol and skatol are oxidized to indoxyl and skatoxyl and then 

 combined with potassium sulphate giving rise to potassium indoxyl sulph- 

 ate and potassium skatoxyl sulphate. Phenol and cresol are apparently 

 directly combined with potassium sulphate. All of these compounds then 

 pass into the blood of the general circulation and finally are eliminated by 

 the kidneys. Potassium indoxyl sulphate or indican is the source of the 

 indigo-forming substance found in the urine. Other compounds are like- 

 wise reduced in toxicity by the liver cells though the methods by which this 

 is accomplished vary with the nature of the compound. The liver thus 

 presents a chemic defense against the entrance of more or less toxic agents 

 into the blood of the general circulation. 



VASCULAR OR DUCTLESS GLANDS. 



INTERNAL SECRETIONS. 



The metabolism of the body generally, as well as that of individual 

 organs, has been shown to be related not only to the physiologic activity 

 of such organs as the liver and pancreas, but also to the activity of the so- 



