294 ABSORPTION -LYMPH AND CHYLE. 



their modifications through the nervous system can not be fully explained. 

 This is true, also, of many of the phenomena of absorption and their modi- 

 fications, which are probably dependent upon the same kind of action. 



It js not necessary to assume the existence of infinitely small openings 

 in homogeneous membranes through which osmotic currents can be made to 

 take place, in order to explain the mechanism of these currents. In the case 

 of two liquids capable of diffusing with each other and separated by an ani- 

 mal membrane, the mechanism of the endosmotic and exosmotic currents is 

 very simple. In the first place, the membrane imbibes both the liquids, but 

 one is always taken up in greater quantity than the other. If water and a 

 solution of common salt be employed, the surface of the membrane exposed 

 to the water will imbibe more than the surface exposed to the saline solution ; 

 but both liquids will meet in its substance. The first step, therefore, in the 

 production of the currents is imbibition. Once in contact with each other, 

 the liquids diffuse, the water passing to the saline solution, and vice versa. 

 This takes place by precisely the same mechanism as that of the passage of 

 liquids through porous septa. 



In no experiments performed out of the body, can the conditions favor- 

 able to the passage of liquids through membranes in accordance with purely 

 physical laws be realized as they exist in the living organism. The great ex- 

 tent of the absorbing surfaces ; the delicacy and permeability of the mem- 

 branes ; the rapidity with which substances are carried on by the torrent of 

 the circulation, as soon as they pass through these membranes ; the uniform- 

 ity of the pressure, notwithstanding the penetration of liquids ; all these 

 favor the physical phenomena of absorption in a way which can not be imi- 

 tated in artificially constructed apparatus. Within the blood-vessels, the 

 albuminoid matters exist in a form which does not permit them to pass 

 through membranes, while the peptones are highly osmotic. The sugars, 

 also, pass through the walls of the vessels with facility, as well as various 

 salts and medicinal substances in solution. The fats, as has been stated, pass 

 mainly into the lacteals, by a process which has already been described and 

 which can not be fully explained by the laws of endosmosis. 



LYMPH AND CHYLE. 



To complete the history of physiological absorption, it will be necessary 

 to treat of the origin, composition and properties of the lymph and chyle. 

 It is only within a few years that physiologists have been able to appreciate 

 the importance of the lymph, for the experiments indicating the great quan- 

 tity of this liquid which is continually passing into the blood are of com- 

 paratively recent date. 



The first successful experiments in which the lymph and chyle were 

 obtained in quantity were made by Colin. This observer, in operating upon 

 large animals, particularly the ruminants, experienced no great difficulty in 

 isolating the thoracic duct near its junction with the subclavian vein and 

 introducing a metallic tube of sufficient size to allow the free discharge of 

 fluid. These experiments, made upon horses and the larger ruminants, were 



