THE PROTOPLASMATIC MEMBRANE 



wound is quickly covered with a fine film. This 

 may be seen very distinctly in the wide cell tubes 

 of the marine alga Caulerpa prolifera. The film- 

 like excretion protects the protoplasm from any 

 further injury from water oozing in. Consequently 

 the whole hyaloplasm layer in the wounded spot is 

 soon regenerated. 



The formation of membranes and of films is, 

 then, a general characteristic of protoplasm and of 

 colloids. This goes so far that it is possible to 

 deprive an albumin solution entirely of its contents 

 of albumin by shaking it. The albumin at once 

 becomes insoluble. We see thus how unstable 

 many colloids are. It has been already men- 

 tioned in a former chapter that a minimum of salt 

 solution is sufficient to precipitate suspension col- 

 loids. But to bring about the flaking out of emulsion 

 colloids by means of salts, we must add com- 

 paratively large quantities of mineral salts. There 

 is no doubt that the effect of salts on emulsion 

 colloids is in many respects allied to the effects of 

 dissolving. Between the particles of the colloid 

 and the salt there must be some solution-affinities 

 which do not exist in suspension colloids. In con- 

 sequence of this characteristic Perrin has proposed 

 to name the suspension colloids Lyophobic Colloids, 

 because there no solution affinities play any part, 

 and to name the emulsion colloids Lyophil Colloids 

 from their connection with real solutions. Durable 

 films are formed especially by precipitated 

 47 



