I40 PROTOPLASMIC ACTION AND NERVOUS ACTION 



tion, while ingenious, does not seem sufficient; in muscle 

 and other living cells immersed in aniso tonic solutions 

 water seems to pass with equal readiness in either direc- 

 tion through the membrane; for example, Arhacia eggs 

 in h>^er- and hypotonic sea w^ater shrink and swell 

 (respectively) at about the same rates.^ Hober refers 

 the difference observed by Bernstein to the greater 

 turgor of the living cells ;^ this explanation also seems 

 doubtful, since turgor is either absent or shght in verte- 

 brate tissues. The simplest as well as most probable 

 explanation is that the permeabihty to water increases 

 with death, along with the permeability to other sub- 

 stances. As the plasma membrane loses its semi- 

 permeability, with the associated fineness of texture, it 

 also loses its relative impermeability to water. 



Permeability to w^ater is one of the little studied 

 properties of cells. Yet it is an important property 

 which appears to be constant for a particular cell under 

 definite conditions. There is evidence that it varies 

 with the physiological state and activity of the cell, 

 and in certain cases, especially in gland cells, the indica- 

 tions are that it is under nervous control. Thus when 

 the chorda tympani is stimulated, the submaxillary gland 

 secretes a copious watery saliva; similarly the sweat- 

 glands and the kidney secrete actively under certain 

 conditions, but not under others. In most cases the 

 secretory substances leave the cell in aqueous solution; 

 and although the factors are complex, there seems to 

 be little doubt that the transport of the secretion across 

 the cell-boundary is associated with an increased permea- 



^ R. S. Lillie, American Journal of Physiology, XLV (1918), 406. 

 =* Hober, op. cit., p. 255. 



