PROTOPLASM 



13 



suspended in the other may vary greatly. Bayliss gives the 



following table to illustrate this : — 



Protoplasm may be regarded as an emulsoid. 



The emulsoids are characterised by showing considerable 

 viscosity. 



Colloids have sometimes been divided into sols when they 

 are fluid, and gels when they are more solid, and there is 

 some evidence that in the latter condition the dispersed 

 phase is the more fluid. (2) It is now known that if a beam 

 of light is allowed to pass through a colloid it is rendered 

 visible — the Faraday-Tyndall phenomenon — whereas when 

 it passes through crystalloids in water it is not seen. (3) If 

 a suspensoid be placed under a microscope, ■ and a ray of 

 light be passed into it along the plane of the stage, it may- 

 be seen to be full of shining, dancing particles. These last 

 two tests indicate the two phases in the colloid. 



This fine subdivision of the two phases introduces an 

 element in the behaviour of a colloid which is not present in 

 the case of a solution, namely, the presentation of an 

 enormous extent of surface between the two phases. It has 

 been calculated that a sphere of gold with a radius of 1 

 millimetre, if subdivided into a gold sol or suspensoid, would 

 present a surface of no less than 100 square metres. This 

 allows of extensive interactions between the phases, and 

 these interactions will depend upon chemical changes in 

 each. Thus great activity of change is rendered possible. 



The phenomena of surface tension between the phases 



