CHAPTER I 

 TURGIDITY 



I. PROTOPLASM AND ITS LIMITING MEMBRANES 



ANYTHING resembling an exact knowledge of the nature 

 of protoplasm is very remote from us as yet, but we may be 

 fairly certain of this, at least, that, whatever else it may be, 

 the vital substance is a mixture of many soluble colloids 

 dissolved in, or impregnated with, an aqueous solution of 

 many different crystalloids. Colloids are very inactive as 

 far as diffusion and osmotic pressure are concerned. Thus, 

 if an internal diffusion tension is developed within a mass 

 of protoplasm, it must be mainly due to the crystalloids dis- 

 solved in the contained water. On this account it must 

 come about that a mass of colloid substance inclosing within 

 its body an osmotic solution, and surrounded by another 

 osmotic solution, will act somewhat as though the former 

 solution were surrounded by a semi-permeable membrane. 

 Because of their slow rate of diffusion, colloid particles must 

 in a measure block the way for the diffusion of crystalloid 

 particles. Hence, if the more concentrated osmotic solution 

 be within the colloid mass, there will be developed a slight 

 osmotic pressure within the mass, which will hasten its 

 normal process of swelling by imbibition. With no truly 

 semi-permeable membrane about it, no state of equilibrium 

 can be attained between a colloid body and the surrounding 

 medium, until, by the slow outward diffusion of the crystal- 

 loid particles and by the entrance of water, there comes 

 about a uniform concentration both within and without. 



In the author's experiments with gelatin plate cultures of 

 Stigeoclonium the following observations were made, which 



49 



