70 PHYSIOLOGY 



particles suspended and the fluid in which they are sus- 

 pended, may allow the existence of a double electric 

 layer. Such a system can hardly be considered a stable 

 one. It has a tendency to pass into one offering the 

 least possible surface. Why is it then that it does not 

 deposit its suspension in flocks, as when we precipitate 

 a proteid. It may be electrical difference which counter- 

 acts this. Surface tension would reach its maximal effect 

 when the difference of potential in the double electric 

 layer fell lowest. 



Solutions of salts usually precipitate colloids ; one 

 method of preparing these latter from their suspensions 

 often called solutions is by salting them out. Various 

 physiologists have suggested that in the limiting 

 stratum between a living cell and the lymph which 

 bathes it there exists a double electric layer. In the 

 case of a contractile cell an amoeboid blood-cell or a 

 muscle-fibre, the double electric layer may be the con- 

 dition which counteracts the tendency for the surface to 

 reduce itself to the smallest possible. The shape of 

 so-called repose of such a cell would be the expression 

 the morphological expression of an equilibrium between 

 the difference of electric potential and surface tension. 

 If a stimulus applied to the cell or muscle consisted as 

 many artificial stimuli do in an electrical charge, if that 

 charge lessened the difference of electric potential, the 

 surface tension would act, and the contractile cell would, 

 its volume remaining the same, approximate to that form 

 with the smallest surface, the spherical form. That is, 

 the muscle would contract. And here comes a differ- 

 ence between precipitation of a non-living colloid and 

 the case of the contraction of a living cell. In the non- 

 living colloid there ensues no subsequent spontaneous 

 resolution the difference of electric potential is not re- 



