44 MATERIA MEDIC A AND THERAPEUTICS. 



II. PHAHMACODYNAMICS. 



Although the liver is apparently so inaccessible, we have 

 great control over the influences under which its multiform 

 activity is displayed. 



(1) By means of the food we can completely interrupt 

 the hepatic functions, or interfere with them at our pleasure. 

 The amount of urea, the secretion of bile, the proportion of 

 store glycogen in *the liver, may dbe modified directly, within 

 certain limits, by the amount of food allowed; and the urea 

 and glycogen may be respectively made to vary with the 

 relative proportion of nitrogenous and amylaceous constituents 

 in the diet. The supply of oxygen which reaches the liver 

 by means of bodily exercise, is equally under our control. 

 The larger the volume of oxygen entering the liver, the more 

 ready and complete will be the subtle processes of chemical 

 composition and decomposition within it. We thus come to 

 appreciate a fact of the first importance that we can influence 

 the liver through the medium of its supply. But we can do so 

 in another way. We can tap, as it were, the channel of supply, 

 the portal vein. The radicals of the portal vein in the rectum 

 (superior ha3morrhoidal) anastomose with the veins around 

 the anus, and leeches applied to this part will drain blood from 

 the portal system, and thus indirectly from the liver. Closely 

 allied to bleeding in principle is hydragogue purgation, which 

 diverts a quantity of water from the portal radicles in the in- 

 testinal wall, and secures its evacuation. 



(2) The liver may be influenced through its products, by 

 securing the proper disposal of the urea, bile, and glycogen. 

 In the bodily organs, as in the practical arts, the rate of 

 manufacture cannot be maintained unless the products be re- 

 moved. We have seen, in the stomach, that digestion is 

 arrested by accumulation of peptones amongst the food. In the 

 like manner, an accumulation of urea, of bile, or of glycogen, 

 in the system, interferes with the hepatic processes. Now, as 

 we shall afterwards see, we can increase the elimination of 

 urea by the kidney, and thus indirectly stimulate the liver. 

 On the same principle, the disposal of the bile furnishes us 

 with a means of rousing the hepatic functions. This brings us 

 to consider the action of indirect cholagogues. 



That portion of the circulation of the bile which occurs in 

 the intestine is thoroughly under our control. We can sweep 

 the bowels empty of its contents; and with these the bile, 

 which otherwise would have been re-absorbed, is expelled from 

 the body. The portal blood and liver are thus deprived of 

 material in which the biliary salts exist ready made, namely, 



