326 THE EQUILIBRIUM OF COLLOID AND 



perimental facts, that the bioplasm holds the crystalloids in loose 

 union in the cell, so that they cannot for the time escape or diffuse 

 out, and yet admits of a degree of molecular freedom to the crystal- 

 loids, so that they still attract water molecules by residual affinity, 

 then we arrive at a conception which is capable of linking together 

 the osmotic properties of the cell, not merely in a statical but in a 

 dynamic way, and gives a basis for understanding the variations 

 in osmotic effects which accompany cell activities from one phase 

 to another. 



With the view of an inert semipermeable membrane of fixed 

 properties, not sharing the varying changes in chemical consti- 

 tution associated with life, or in other words not possessing the 

 properties of bioplasm outlined above, all that can be arrived at is 

 a continual tendency in one direction to a fixed equilibrium. 



The other view, that the osmotic properties are developed by 

 the bioplasm itself in its varying unions with crystalloids, gives 

 room for that up-and-down play of properties which is the out- 

 standing characteristic of living matter. 1 



For example, a circulating hormone, a drug substance, or a 

 nerve impulse arriving at a given set of cells in a tissue, may activate 

 the cells by momentarily disrupting unions between bioplasm and 

 crystalloids or the reverse, and so may cause an uptake or a giving 

 out of water accompanied by certain crystalloids free in excess to 

 or from the cell, or may alter water distribution in varying parts 

 provoking muscular contraction or other form of protoplasmic 

 movement. 



Similarly molecular movements of radicles attached to the 

 bioplasm may be induced, causing changes in molecular arrange- 

 ment and synthesis of new bodies within the cell. Further, the 

 osmotic pressures and concentrations of the crystalloids and other 

 bodies so set free need obviously bear no immediate relationship 

 to the concentration of these substances in the plasma outside the 

 cell, and so the very varying concentrations of secretions may be 

 understood in a way that cannot be realised on any basis of pure 

 osmosis or filtration. 



The experimental facts of cell life, both in regard to the taking 



1 It is interesting to note that serum proteins exactly at their neutral 

 point show no osmotic pressure whatever, but addition of minute amounts 

 either of acid or alkali at once gives rise to an osmotic pressure which up to 

 certain limits increases with amount of acid or alkali added. 



