456 



SCIENCE 



[X. S. Vol. XXXII. 'No. 823 



It is thus seen how in a system like that 

 of a drop of water with different contact 

 surfaces the surface tension is affected and 

 how this alters the distribution of solutes. 

 It is further to be noted that for most or- 

 ganic solutes the action in this respect is 

 the very reverse of that of inorganic salts. 

 Consequently, in a living cell which con- 

 tains both inorganic and organic solutes, 

 and in which there are portions of differ- 

 ent composition and density, the equilib- 

 rium may be subject to disturbance con- 

 stantly through an alteration of the 

 surface tension at any point. Such a dis- 

 turbance may be found in a drop of an 

 emulsion of olive oil and potassium car- 

 bonate in the well-known experiments of 

 Biitschli. When the emulsion is appro- 

 priately prepared, a minute drop of it, 

 after it is surrounded with water, will 

 creep under the cover glass in an amceboid 

 fashion for hours, and the movement wiU 

 be more marked and rapid when the tem- 

 perature is raised to 40 to 50° C. All the 

 phenomena manifested are due to a lower- 

 ing of the surface tension at a point on 

 the surface, as a result of which there is 

 protrusion there of the contents of the 

 drop, accompanied, Biitschli holds, by 

 steaming cyclic currents in the remainder 

 of the mass. 



Surface tension also, according to J. 

 Traube, is all-important in osmosis, and he 

 holds that it is the solution pressure 

 (Haftdnick) of a substance which deter- 

 mines the velocity of the osmotic movement 

 and the direction and force of the osmotic 

 pressure. The solution pressure of a sub- 

 stance is measured by the effect that sub- 

 stance exercises when dissolved on the sur- 

 face tension of its solution, or, to put it in 

 Traube 's own way, the more a substance 

 lowers or raises the surface tension of a sol- 

 vent (water) the less or greater is the solu- 

 tion pressure (Haftdruck) of that sub- 



stance. This solution pressure, Traube 

 further holds, is the only force controlling 

 osmosis through a membrane, and he re- 

 jects completely the bombardment effect 

 on the septum postiilated in the van't Hofif 

 theory of osmosis. 



The question as to the nature of the fac- 

 tors concerned in osmosis must remain un- 

 decided until the facts have been more 

 fully studied from the physiological stand- 

 point, but enough is now known to indicate 

 that surface tension plays at least a part 

 in it, and the omission of all consideration 

 of it as a factor is not by any means a 

 negligible defect in the van't Hoff theory 

 of osmosis. 



The occurrence of variations in surface 

 tension in the individual cells of an organ 

 or tissue is difficult to demonstrate directly. 

 We have no methods for that purpose, and, 

 in consequence, one must depend on in- 

 direct ways to reveal whether such varia- 

 tions- exist. The most effective of these is 

 to determine the distribution of organic 

 solutes and of inorganic salts in the cell. 

 The demonstration of the former is at 

 present difficult or even in some cases im- 

 possible. The occurrence of soaps which 

 are amongst the most effective agents in 

 lowering surface tension may be revealed 

 without difficulty microehemically, as may 

 also neutral fats, but we have as yet no 

 delicate microchemical tests for sugars, 

 urea, and other nitrogeneous metabolites, 

 and in consequence the part they play, if 

 any, in altering the surface tension in dif- 

 ferent kinds of cells, is unknown. Further 

 research may, however, result in discover- 

 ing methods of revealing their occurrence 

 microehemically in the cell. We are in a 

 like difficulty with regard to sodium, whose 

 distribution we can determine microehem- 

 ically in its chief compounds, the chloride 

 and phosphate, only after the exclusion of 

 potassium, calcium and magnesium. We 



