ABSORPTION. 257 



simply to known endosmotic relations. We shall meet with a 

 considerable number of substances which, although they are ex- 

 tremely soluble, and occur in very dilute solution, are unable to 

 enter directly into the intestinal capillaries, while there are many 

 substances which only reach the blood indirectly through the 

 lacteals. Although such facts as these strike us at the first glance 

 as singular, we must not forget that the relations existing between 

 the dissolved parts of the intestinal contents and the veins of the 

 intestine are less simple than the above description might lead us 

 to infer. These fluids, and the walls of the intestinal capillaries, 

 are separated by at least one dense layer of epithelial cells, which 

 are further surrounded by a more or less dense network of 

 filaments of connective tissue. We are unable at the present time 

 to determine what modifications these thick layers of organic 

 matter induce through the results of endosmosis, and consequently 

 also of absorption, but that they do effect such changes has been 

 proved beyond a doubt by numerous experiments on endosmosis, 

 which agree in showing that an endosmotic motion is succeeded by 

 numerous alterations depending upon the thickness of the mem- 

 brane,its morphological and chemical character, the chemical consti- 

 tution of the fluids between which the interchange is going on, &c. 

 We know that the difference between animal membranes exerts an 

 essential influence on the endosmotic process, although we are 

 still far from knowing how a mucous membrane, a serous mem- 

 brane, &c., is able to induce or to modify an endosmotic process. 

 We know, further, that external pressure powerfully influences 

 endosmosis; and Liebig's beautiful investigation affords an example 

 how, in consequence of different pressure, we obtain an opposite 

 result from what the fundamental principles of endosmosis would 

 have led us to expect; but we are not acquainted with any mathe- 

 matical connection between the amount of the pressure and the 

 velocities of endosmotic motion. The influence exerted by the force 

 of different pressures is of the greatest importance in the process 

 of absorption by the intestinal capillaries, for we need scarcely 

 observe that the pressure to which the blood is exposed in the 

 capillaries must contribute very essentially towards the abundant 

 absorption of matters from the dilute solution of the chyme- 

 constituents. If we know the law of endosmosis, in its simplest 

 expression, we are still totally unable to classify according to 

 simultaneously prevailing conditions and definite general formulae, 

 the differences of its actions. Notwithstanding the efforts of the 

 most distinguished inquirers, such as Poisson, Magnus, Briicke 

 VOL. III. S 



