ABSORPTION OF FATS AND INSOLUBLE SUBSTANCES. 461 



evident that under certain circumstances, fatty emulsions 

 must be endosmotic, or, in other words, they are capable 

 of passing through membranes. 



It is true that the currents which take place between two 

 miscible liquids of different densities separated by an animal 

 membrane do not usually occur when one of these liquids is 

 a fatty emulsion ; and this is explained by the general law that 

 all substances, in order to pass through membranes, must be 

 in solution. It must be remembered, however, that we can 

 but roughly imitate the physiological conditions of any func- 

 tion, in experiments out of the organism. In an endos- 

 mometer, we usually have two liquids of different densities 

 separated by the membrane, and the currents are dependent 

 upon very simple physical laws. In the organism, the blood 

 is moving with great rapidity in vessels possessing contrac- 

 tile and elastic coats ; the diameter of the vessels is subject 

 to great variations ; the liquids which enjer the blood-vessels 

 or the lacteals pass through epithelial cells and other struc- 

 tures which are in a condition of continual metamorphosis ; 

 the walls of the vessels are thinner than any membrane which 

 we can make use of ; and there is a host of conditions which 

 cannot be fulfilled in any apparatus that can be artificially 

 constructed. We may roughly imitate the movement of the 

 circulating fluids, and then it is found that the activity of 

 the endosmotic current is greatly increased. 



It has been found, also, that the chemical reaction of 

 the endosmotic liquids has an important influence upon 

 osmotic currents. This latter condition is most interesting 

 with regard to the absorption of fats. While it has been 

 found invariably that neutral emulsions will not pass through 

 membranes and mix with pure water or with neutral fluids, 

 it has been conclusively demonstrated by Matteucci that the 

 passage of fats readily takes place when both of the solutions 

 are alkaline. This observer, having made an emulsion of 

 olive-oil with water containing 4*3 parts per thousand of 

 potash, introduced into it an endosmometer likewise filled with 



