July 28, 1911] 



SCIENCE 



103 



suiting emulsion is firm enough to handle 

 with a shovel. A firm system of this sort 

 is used technically as a lubricant. By the 

 emulsification of certain heavy oils with 

 less than one per cent, of water an emul- 

 sion so solid may be formed from the two 

 liquids that it maybe whittled with a knife.' 

 These considerations, however, do not tell 

 the whole story, at any rate for plants. 

 A part of the firmness of many plant struc- 

 tures is due to the phenomenon termed by 

 plant physiologists "turgor." This phe- 

 nomenon has much similarity to the infla- 

 tion of a flabby, hollow, elastic balloon with 

 gas. In turgor, however, the inflation is 

 by water, not gas, and the inflating force is 

 not mechanical but osmotic. How far tur- 

 gor is responsible for rigidity in animal 

 structures is not yet clear. Certainly some- 

 thing very similar exists in the red blood 

 corpuscles. 



We have been considering the concentra- 

 tration of substances upon surfaces of 

 finely subdivided phases; but in obedience 

 to the same laws concentration takes place 

 upon larger surfaces. This phenomenon 

 must occur not merely at the contact sur- 

 faces between the phases in the interior, 

 but also upon the outer surface of the pro- 

 toplasmic mass itself. In such places we 

 must have a concentration of material. 

 Indeed, it can be shown experimentally that 

 many solutions form really quite firm mem- 

 branes even when there is no chance for 

 evaporation to take place.^ Very probably 



' Ostwald, Wo., op. cit., p. 105. 



'Eamsden, W., "Abscheidimg fester Korper in 

 den Oberflaehensehichten von Losungen und ' Sus- 

 pensionen' " (Beobachtungen uber Oberflachen- 

 hiiutchen, Emulsionen und mechanische Koagnla- 

 tion), Zeitschrift fur physikalische Chemie, Bd. 

 47, 8. 336. 



Metealf, M. V., "Ueber feste Peptonhiiutchen 

 auf einer Wasserflaehe und die Ursache Ihrer 

 Entstehung," ibid., Bd. 52, S. 1. 



Zangger, H., "Die Immunitats-Eeaktionen als 

 physikalisches spez. als Colloid-Phanomen, " Vier- 



this phenomenon is responsible in many in- 

 stances for the formation of biological 

 membranes and may also account for the 

 differentiation of the external layer so fre- 

 quently seen in cells. This might merely 

 be the result of the concentration of ma- 

 terial in the outside layer in consequence 

 of surface action." Considerable evidence 

 for the participation of surface forces in 

 cell-membrane formation may be found in 

 the studies on hemolysis, by which is meant 

 the leaking of hemoglobin through the 

 membranes of blood corpuscles. Many of 

 the substances which cause the cell mem- 

 branes of the red blood corpuscles to lose 

 their semi-permeability in this way, have a 

 great influence on surface tension. Such 

 are soaps and saponine. One of the ac- 

 tions of certain snake venoms is dependent 

 upon the presence in the venom of a sub- 

 stance of this type.^" 



If this hypothesis of concentration of 

 material at the cell surface be correct, then 

 it is easy to understand how many cells 

 have the power of regenerating a new 

 membrane on a wound surface, such as is 

 formed when an amceba is cut in two. The 

 surface energies must begin at once to act 

 at the new surface until it, too, has been 

 brought into equilibrium with the interior 

 just like the rest of the cell surface. ^^ 



This hypothesis of membrane formation 

 can not be applied, for the present, at any 

 rate, to many specialized membranes such 



teljahreschrift der Natnrforschenden Gesellschaft 

 in Ziirich, Jahrgang 35, S. 441. 



'Overton, E., "Ueber den Mechanismus der Ee- 

 sorption und der Sekretion in W. Nagel 's ' Hand- 

 buch der Pliysiologie des Menschen, ' " Band II., 

 Teil II., Seite 805-6. 



Pfeflfer, W., " Osmotische Untersuehungen, Stu- 

 dien zur Zellmeebanik, " S. 124, Leipzig, 1877. 



'° Zangger, H., ' ' Ueber Membranen und Mem- 

 branf unktionen, " Ergebnisse der Physiologie, Bd. 

 7, S. 138, 1908. 



" Gf . Overton, op. cit.; Pfeffer, op. cit., and 

 Zangger, op. cit. 



