PASSAGE OF LIQUIDS THEOUGH MEMBEANES. 475 



the endosmometer ; which consists simply of a small bell 

 glass, the lower opening of which is closed by a membrane, 

 the opening above being connected with a long glass tube 

 by which the force with which liquids pass through the 

 membrane can be measured. The bell-glass is generally filled 

 with a liquid capable of attracting a current of water from 

 without, and is immersed in pure water, so that the membrane 

 is completely covered. Under these circumstances, there is 

 a current of water through the membrane, which will cause 

 the liquid to mount in the tube, sometimes to the height of 

 several feet; but at the same time, there is a feebler current 

 from the interior of the apparatus to the water. Dutrochet 

 called the stronger, the endosmotic current, and the feebler, 

 the exosmotic current. This nomenclature, however, is not 

 strictly accurate ; for if the position of the liquids be re- 

 versed, as was shown in the old experiments of Nollet, the 

 stronger current is exosmotic and the feebler is endosmotic. 

 It must be remembered, therefore, that the name endosmosis 

 is always to be understood as applied to the principal cur- 

 rent, while the term exosmosis is applied to the current in 

 the opposite direction. This possible inaccuracy of expres- 

 sion has led to the adoption by Graham and others of the 

 term osmosis, as applied generally to the currents which take 

 place through membranes ; a but the terms first proposed by 

 Dutrochet are most commonly used. 



The phenomena of endosmosis, w^hich, since the publica- 

 tion of the researches of Dutrochet, have been so closely 

 studied by physicists, are chiefly interesting to the physiolo- 

 gist in their application to absorption. "While it is perhaps 

 true that all the phenomena of physiological absorption 



that little organic vesicles, when immersed in water, discharged a portion of their 

 contents through their investing membranes. This fact he communicated to the 

 Philomathic Society of Paris, in 1809 (pp. cit., p. 5), but as we have already seen, 

 essentially the same phenomenon was observed in an egg by Parrot, in 1802. 



1 GRAHAM, On Osmotic Force. Philosophical Transactions, London, 1854, p. 

 177 et seq.; and Elements of Inorganic Chemistry, Philadelphia, 1858, p. 746. 



