610 SPECIAL PHYSIOLOGY. 



as the force of capillary attraction ; that is, where the greatest capil- 

 lary attraction exists, there less pressure is required."* 



It has heen the object of numerous researches by Dutrochet, Mat- 

 teucci, Liebig, Vogel, Prof. Graham, and others, to ascertain the phys- 

 ical causes and vital influences determining this process ; and as the 

 result of their labors, it has been pretty well determined that osmosis 

 depends, in the first place, upon two essential conditions, but is further 

 influenced by several causes. 



The first essential condition of osmosis is a greater affinity of one fluid 

 for the membrane over that of the second fluid for the same membrane, 

 that is, one fluid must have a greater power of wetting the membrane 

 than is possessed by the other fluid. If such does not exist, no cur- 

 rent will be developed. It is plain that this imbibition, or wetting of 

 the membrane by the fluids, is nothing else than an effect of capil- 

 larity, the property possessed in various degrees by fluids, of ascend- 

 ing very fine hair-like tubes, here provided by the meshes of the 

 membrane. That different fluids possess a different power in this re- 

 spect was shown by Liebig, who found that 100 parts of ox-bladder 

 took up in 24 hours 



Of pure water, 268 vols. 



" saturated solution of sea salt, . . 133 " 



" alcohol of 84 per cent., . . 38 " 



" oil of marrow, . . . 17 " 



That such different affinity exists not only on the part of different 

 fluids for the same membrane, but also of the same fluid for different 

 membranes, may be shown by the following experiment : Let three open 

 tubes be covered at one extremity with a piece of pig's bladder, and 

 filled with water, alcohol, and ether, respectively ; three others cov- 

 ered similarly by india-rubber, filled with the same fluids, and all be in- 

 verted in a basin of mercury. After an interval of a few hours, it 

 will be found that the mercury has risen in the tube covered with 

 bladder and containing water, to a very appreciable height, while in 

 the tube containing ether it has risen but slightly, and in that containing 

 alcohol scarcely at all. The water, having a great affinity for the mem- 

 brane, wets it rapidly, and is evaporated from its outer surface, while 

 the mercury rises in the interior to take its place. The alcohol and ether, 

 having but little affinity for the membrane, are not rapidly removed. 

 In the tubes covered with india-rubber, the reverse will be found to 

 have taken place. Here the alcohol having a great affinity for the 

 membrane, wets it, and is evaporated from the outer surface, causing 

 the mercury to rise in its place. This will explain the phenomena 

 so familiar to those who are conversant with the preservation of ana- 

 tomical preparations in alcohol. When the jars in which specimens 

 are immersed are covered with bladder, the water evaporates and the 

 alcohol becomes stronger; while if the jar be covered with india-rubber, 

 the alcohol evaporates and that which remains becomes diluted. 



It thus appears that the portion of the process of osmosis which 



* Carson Osmosis : its Agency in Action of Medicines, &c. A Review, Am. 

 Jour. Med. Sci., July, 1865, p. 139. 



