838 BIOPHYSICAL PHENOMENA [pt. iii 



of Kite and of Chambers, who had stated that the ooplasm was just 

 viscous enough to put a stop to Brownian movement. During 

 mitosis the marked changes in viscosity led to a local lowering of 

 viscosity to vv 3 or thereabouts, Seifriz's later experiments were very 

 ingenious. He introduced by the aid of a micromanipulator a 

 minute nickel ball about 7jLt in diameter into the cytoplasm of the 

 Ggg of the sand-dollar, Echinarachnius parma (a principle that had been 

 adopted in the work of Freundlich & Seifriz on inorganic colloids) . 

 The particle having been introduced, it was attracted by a powerful 

 electromagnet, until the colloid was stretched a certain amount. If 

 this amount was not exceeded the particle would return to its 

 original position when the current was cut off. The distance over 

 which the particle travelled furnished a measure of the stretching 

 capacity of the colloidal substance, and the force necessary to pro- 

 duce the stretching was a measure of the elasticity. It was found 

 that a particle introduced into the protoplasm of an Echinarachnius 

 egg could be moved backwards and forwards through the inner 

 parts by the electromagnet, apparently without any injury being 

 done, but that, when it came up against the cortical parts of the egg, 

 its motion was much slower and might completely cease. Obviously 

 their viscosity was greater. Quantitative calculations showed that 

 the vv of the inner part was just the same as that which Seifriz had 

 previously allotted to other marine eggs, i.e. barely that of con- 

 centrated glycerine (sp.g. 1-2500). The stretching distance of the 

 cortex protoplasm was 9 /a. Nothing has since been done to follow 

 up this interesting type of investigation, but various investigations of 

 viscosity in echinoderm eggs have been made (Barth ; Jacobs ; etc.) 

 and for further information the monograph of Heilbrunn should be 

 consulted. 



