chap, xxn.] DIURESIS AND CATHARSIS. 265 



more salt than the blood, a more or less decided 

 catharsis ensues." 



That is to say, that in the first case there was 

 rapid passage of a large quantity of water into the 

 blood, and a consequent activity of the excretory 

 action of the kidney to throw it out. In the second 

 case, the proportion of salt being the same on both 

 sides of the animal membrane, though mixture took 

 place by diffusion, or otherwise, there was no marked 

 change in the volume of fluid on either side of the mem- 



^ 



brane. In the last case the proportion of saline matter in 

 the draught was proportionately so much greater than 

 that in the blood, that a current, the reverse of that 

 in the first case, was set up, determining a flow of 

 serum from the blood-vessels into the cavity of the 

 intestines. Simultaneous with that flow, there was of 

 course the passage of certain of the saline constituents 

 of the draught into the blood, but the prominent 

 occurrence was the outward flow of serum. 



What has been said of the physics of absorption 

 from the intestinal canal, is equally applicable to 

 absorption from serous cavities, or from areolse of the 

 tissues, where practically the same conditions are 

 present. Variations in the rapidity of absorption by 

 different tissues can to a large extent be explained by 

 the facts that are known as to the differences in ab- 

 sorptive power of various membranes, depending on 

 their thickness, their density, and other similar cir- 

 cumstances. 



Circumstances also may be present which seriously 

 impede the progress of the process of eiidosinosis. Even 

 as hydrochloric acid has been seen to have the power 

 to determine the direction of the current, to impede it 

 in one direction and to aid it in another, so there are 

 other substances which act inversely to hydrochloric 

 acid, and retard the process from the cavity, intestinal 

 canal, or other part, inwards to the blood. There are 



