VARIATIONS AND MODIFICATIONS OF ABSORPTION. 291 



It has been shown that liquids which immediately disorganize the tissues, 

 such as concentrated nitric or sulphuric acid, can not be absorbed. Another 

 important peculiarity in absorption is that solutions which readily coagulate 

 the albumen of the circulating fluids are absorbed very slowly (Miahle). 

 This is explained by the supposition that there is a coagulation of the albu- 

 minous fluids with which the absorbing membrane is permeated, which in- 

 terferes with the passage of liquids. These substancs are nevertheless taken 

 up by the blood-vessels, though rather slowly. 



Influence of the Condition of the Blood and of the Vessels on Absorption. 

 After loss of blood or deterioration of the nutritive fluid from prolonged 

 abstinence, absorption generally takes place with great activity. This is well 

 known, both as regards the entrance of water and alimentary substances and 

 the absorption of medicines. It was at one time quite a common practice to 

 bleed before administering certain remedies, in order to produce their more 

 speedy action upon the system. 



The rapidity of the circulation has an important influence in facilitating 

 absorption, and this process is generally active in proportion to the vascu- 

 larity of different parts. During intestinal absorption, the increase in the 

 activity of the circulation in the mucous membrane is very marked and un- 

 doubtedly has an influence upon the rapidity with which the products of di- 

 gestion are taken up by the blood. 



Influence of the Nervous System on Absorption. It is certain that ab- 

 sorption, especially in the stomach, is subject to certain variations, which can 

 hardly be dependent upon anything but nervous action. Water and other 

 liquids, which usually are readily absorbed from the stomach, are sometimes 

 retained for a time, and are afterward rejected in nearly the condition in 

 which they were taken. It is probable, however, that the most important 

 influences thus exerted by the nervous system are effected through the circu- 

 lation. The experiments of Bernard and others upon the vaso-motor nerves, 

 by the action of which the supply of -blood in different parts is regulated, 

 point out a line of experimentation which would probably throw much light 

 upon some of the important variations in absorption. When it is remem- 

 bered that the small arteries may become so contracted under the influence 

 of the vaso-motor nerves that their caliber is almost obliterated, of course re- 

 tarding in a corresponding degree the capillary and venous circulation in the 

 parts, and again, that the same vessels may be so dilated as to admit to a par- 

 ticular part many times more blood than it ordinarily receives, it becomes 

 apparent that absorption may be profoundly affected through this system of 

 nerves. It has been ascertained that while a section of some of the nerves 

 distributed to the alimentary canal will slightly retard the absorption of the 

 poisonous substances, the process is never entirely arrested. 



IMBIBITION AND ENDOSMOSIS. 



If liquids pass through the substance of an animal membrane, it is evident 

 that the membrane itself must be capable of taking up a certain portion by 

 imbibition ; and this must be considered as the starting-point in absorption. 



