ELECTRO-CHEMICAL SURFACE-TENSION THEORY 117 



similar evidence would lead us to conclude that glycerine and alcohol 

 were also co-operative factors. 



The shock-stoppage produced by so many agencies when suddenly 

 applied may be the result of a temporary disturbance of the organized 

 arrangement of the protoplasmic particles, supposed on the above 

 hypothesis to be necessary for streaming. Mechanical stimuli, for example, 

 might readily exercise some such action, although we might expect to 

 find in this case, not a complete stoppage but irregular streaming 

 in various directions for a time. The stoppage might also be due to 

 sudden changes of surface-tension, produced first in the outer layers of 

 protoplasm. The effect of these would be to give the protoplasm a 

 tendency to move bodily inwards or outwards as the case might be. The 

 former movement is prevented by the internal osmotic pressure, the latter 

 by the cell-wall ; but the effect would be to exercise a temporary drag 

 upon the protoplasmic particles, which might be sufficient to arrest their 

 movement. 



These are, however, merely theoretical suggestions which may serve 

 to stimulate inquiry, or which may afford a framework of hypothesis on 

 which to hang facts. It is a fundamental error to suppose, as Hofmeister 

 (1. c., p. 63) and Engelmann (1. c., p. 373) have done, that all protoplasmic 

 movement must be produced in the same manner, that is by the interaction 

 of precisely similar forms of energy with the same motor-mechanism. 

 Even in the same cell the movement of a pulsating vacuole may have 

 a different physical origin to that of streaming in neighbouring parts. 

 Similarly the physical conditions in protoplasmic threads crossing the 

 cell-sap are not the same as in the layers of protoplasm pressed against 

 the cell-wall. It is true that transitions occur from sliding movements 

 to circulation, and from circulation to rotation ; but it is equally possible 

 that more than one form of energy may be concerned, and that the motor- 

 mechanism may include factors essential at certain times or in certain 

 cases but not in all. 



Just as all engines are not alike, nor are they all driven by steam, so 

 also do different protoplasts differ in their internal constitution, and hence 

 also in the manner in which they can utilize different forms of energy. 

 Thus temporary localized sliding movements might easily be due to localized 

 differences of surface-tension produced by irregular diffusion or by chemical 

 action. Such movements might ultimately be aided or overpowered by 

 those produced by the continuous interaction of electrical and surface- 

 tension energy, and so regular streaming or rotation be produced. 



Whatever the mechanism may be, the living organism exercises a cer- 

 tain controlling influence upon it : hence it does not necessarily follow that 

 a chemical or physical agency will produce the same effect within a living 

 cell that it does outside it. Moreover, a stimulus which retards streaming 



