\ 



Dandeno : Osmotic theories 285 



tion to show that we need more definite statements with regard to 



the subject. We 



if tlie quotations 



above can be taken as representative of them — because there is 

 no subject more fundamental, more universal in plant and animal 

 functions, than osmosis. And it is in this connection that we need 

 something more definite than we have. The physiologist is con- 

 fronted with osmotic phenomena at every turn, and he looks in 

 vain for explanations which will satisfy the conditions he meets. 

 Some theories meet with one condition, but not another. 



We regard to osmotic pressure, it should be said that no defi- 

 nite measurements were made of it until Pfeffer * developed an 

 apparatus based in its mechanism on the plant cell, but made of 

 niorganic material, and capable of measuring the pressure set up 

 by osmotic forces. Pfeffer's work was epoch-making in this re- 

 spect, and practically all development made on osmotic measure- 

 ments, both theoretical and experimental, has been based on 

 PfeiTer's researches. The apparatus which Pfefifer prepared has 

 been known as the ** Pfeffer cell." This cell is composed of a 

 porous earthenware cup like a battery jar, in the walls and bottom 

 of which is a precipitate of copper ferrocyanide. This jar, when 

 plugged and connected with a manometer, can be used to measure 



r 



the pressure produced by osmotic action of certain given sub- 

 stances. This cell, though easily described, is extremely difficult 

 to make, and in very few laboratories, so far as the writer can learn, 

 has the Pfeffer cell been made to work successfully. Comparatively 

 recently, however, the Pfeffer cell has been improved to a high 

 degree by Morse and colleagues f at Johns Hopkins University, and 

 used with great success on osmotic pressure investigations. The 

 improvement to the Pfeffer cell has been mainly in the matter of 

 extracting the air from the porous jar, and placing the membrane. 

 This is done by means of an electric current which forces the 

 liquid into the wall of the jar. The insertion of the stopper plug 

 is a difficult operation also ; in fact, where high pressures are to 

 be recorded, the whole operation is one which requires the greatest 

 care in every detail, and one which taxes tlie patience of the oper- 

 ator to the utmost. Morse and Frazer succeeded in preparing: a 



* Osmotische Untcrsuchungeti. 1877. 



f Am. Chem. Jour., vols. 26, 28, 34, and others. 



