328 



PROTOPLASM 



phenomenon by means of extension - currents which have 

 their seat at the boundary between the cell-sap and the 

 protoplasm of the wall. We found before that it is possible 

 to set up such a rotational current in an oil-drop, if by means 

 of proper precautions care be taken that the extension- 

 current only attains to development upon one side (see 

 above, p. 74). Of course this phenomenon presupposes that 

 there is, as a matter of fact, only a single powerful centre 

 of extension -currents present in a state of permanent 

 activity, which produces the current ; for as I have already 

 explained earlier, I cannot regard as correct Berthold's idea 

 of the origin of such a rotational current by the conflict of 

 numerous currents. If we now assume such a centre of 

 extension-currents in a definite position, as the cause of the 

 rotational current on the inner surface of the protoplasm 

 lining the wall, the question arises, why the current in this 



case is developed only on one side, and 

 thus leads to rotation. In reference to 

 this point Quincke (1888) has already 

 remarked that it must occur if, by means 

 of solid particles or by a partial rigidity of 

 its surface, an obstacle to the development 

 of the current on one side is present. In 

 our earlier described experiment the glass 

 surface, to which the oil -drop adhered, is 

 the obstacle. Hence if we assume that 

 on the inner surface of the protoplasm 

 lining the wall of a cell, somewhere 

 at the surface of one end, near x (see 



Fig. 23. 



Fig. 23), such an obstacle is present in the form of 

 a narrow solid bridge, stretched out over the proto- 

 plasm of the surface of this end, then an extension-current, 

 the centre of which is placed along one side of this solid 

 bridge, will naturally become a one-sided rotational current, 

 circulating in the cell in the direction of the arrows. 

 The question now is whether arrangements really exist which 

 make it probable that conditions of this kind are realised in 

 rotation currents. I am only aware of one case to refer to 

 in this respect, which at least yields the possibility of such 



