360 LEWIS V. HEILBRUNN. 



into the membrane, and thus lower its surface tension. More- 

 over, because of their inability to penetrate the membrane, they 

 exert pressure against it, osmotic or otherwise. Secondly, coagu- 

 lative agents prevent membrane elevation, since they make it 

 impossible for the protein which causes the phenomenon to swell. 

 Probably the main reason that glycerin and sugar solutions do 

 not produce membrane elevation is their action in increasing the 

 viscosity of the gels. 1 When the viscosity of the membrane is 

 augmented, it loses its fluidity and can no longer be pushed out. 

 This hardening effect can be observed directly by placing fer- 

 tilized eggs with membranes in a sugar solution and examining 

 the result under the microscope. 



When acids are used to produce membrane elevation, a return 

 to sea-water is usually necessary. No doubt, the acid by virtue 

 of its coagulative power inhibits membrane elevation. On a 

 return to sea-water the coagulative effect is lost by dilution, but 

 enough acid has probably been adsorbed by the membrane to 

 lower its surface tension sufficiently for membrane elevation. 



For the sake of simplicity, one of the factors which must have 

 an influence on membrane elevation has been omitted from the 

 discussion. It has been shown 2 that in the presence of chlorides, 

 bromides or nitrates, gelatine shows a greater tendency to swell 

 than in pure water, but that sulphates, sugar, and glycerin have 

 a retarding effect. If membrane elevation is the result of the 

 swelling of a colloid, and if this colloid behaves as gelatine, the 

 presence of chlorides, bromides, and nitrates would accelerate 

 the process, whereas sugar and glycerin would retard or prevent 

 it. The effect of these substances is probably of secondary 

 importance. 



In the course of the argument, evidence has been adduced 

 which may also serve to explain other biological problems. Al- 

 though the toxicity of distilled water has often been noted, no one 

 has ever offered a satisfactory explanation. Bullot 3 found that 

 the purest water obtainable (redistilled in platinum and quartz) 

 was toxic to the fresh water Gammarus. It is believed that this 



1 Leick, Drude's Annalen, XIV., 139 (1904). 



2 See Freundlich, " Kapillarchemie," p. 512. 



3 G. Bullot, Univ. Cal. Pub. Physiol., I., 199 (1904). 



