TRANSUDATION THROUGH ANIMAL TISSUES. 361 



mingled, to a certain extent, with each other. A part of the salt will 

 have passed into the distilled water, giving it a saline taste ; and a part 

 of the water will have passed into the saline solution, making it more 

 dilute than before. If the quantities of the two liquids, which have 

 become so transferred, be measured, it will be found that a comparatively 

 large quantity of water has passed into the saline solution, and a com- 

 paratively small quantity of the saline solution has passed out into the 

 water. That is, the water passes inward to the salt more rapidly than 

 the salt passes outward to the water. The consequence is, that the 

 saline solution is increased in volume, while the water is diminished. 

 The more abundant passage of the water, through the membrane to the 

 salt, is called endosmosis ; and the more scanty passage of the salt out- 

 ward to the water is called exosmosis. 



The mode usually adopted for measuring the rapidity of endosmosis 

 is to take a glass vessel, shaped somewhat like an inverted funnel, wide 

 at the bottom and narrow at the top. The bottom of the vessel is 

 closed by a thin animal membrane, stretched tightly over its edge and 

 secured by a ligature. From the top of the vessel there rises a narrow 

 glass tube, open at its upper extremity. When the instrument is thus 

 prepared, it is filled with a saline or saccharine solution and placed in a 

 vessel of distilled water; so that the membrane, stretched across its 

 mouth, shall be in contact with pure water on one side and with the 

 interior solution on the other. The water then passes in through the 

 membrane, by endosmosis, faster than the ingredients of the solution 

 pass out. An accumulation consequently takes place inside the vessel, 

 and the level of the fluid rises in the upright tube. The height to which 

 the fluid thus rises in a given time is a measure of the intensity of the 

 endosmosis, and of its excess over exosmosis. By varying the consti- 

 tution of the two liquids, and the arrangement of the membrane, the 

 variations in endosmotic action under different conditions may be 

 readily ascertained. Such an instrument is called an endosmometer. 



Physical Conditions influencing Endosmosis. The conditions which 

 regulate the intensity and extent of endosmosis have been investigated 

 by Dutrochet, Graham, Yierordt, Matteucci, and Cima. The first of 

 these conditions is the freshness of the animal membrane. A mem- 

 brane that has been dried and moistened again, or one that has begun 

 to putrefy, will not produce its full effect. It is also found that if the 

 membrane be allowed to remain and macerate in the fluids, after the 

 column has risen to a certain height in the upright tube, it begins to 

 descend again when putrefaction commences, and the two liquids finally 

 sink to the same level. 



The next condition is the extent of contact between the membrane 

 and the two liquids. The greater the extent of contact, the more rapid 

 is endosmosis. An endosmometer with a wide mouth will produce 

 more effect than with a narrow one, though the volume of liquid may 

 be the same in both instances. The action takes place in the substance 

 of the membrane, and is proportional to its extent of surface. 

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