6 Hydration and Growth. 



to writers who view matter and all material conceptions from a remote 

 distance. Colloids, with their electrical charge, absorptive and adsorp- 

 tive properties, and molecular arrangement, display a series of char- 

 acters fundamental to organic growth, of which swelling as a resxolt of 

 hydration is one of the most noticeable, which do not extend to crystals. 



Furthermore, the colloidal systems which are exemplified in living 

 or organic material are rarely at rest in the sense of which this may be 

 said of crystals. It is true, of course, that substances or formations 

 may occur in nature or in the laboratory which are made up of both 

 crystalline and colloidal material, and it is also true that some com- 

 pounds may pass from one condition to the other, but the action by 

 which a crystal is formed is not one coincident with colloidal reactions, 

 nor does the perfect crystal behave like a mature cell, organ, or organ- 

 ism. In fact, the more perfect a crystalline structure may be, the 

 farther does it depart from the state in which it might display activities 

 or enlargements similar to those of growth of living matter. 



The essential feature of an idealized growth is the accretion or addi- 

 tion of water and material to the mass of colloid constituting the cell. 

 The actual mechanism of incorporation is not easily delineated. If 

 protoplasm consisted of a system of colloidal structures such as those 

 of the pentosans and the proteins interwoven but not diffusing into 

 each other, the more soUd material which lowers the surface tension to 

 the greatest extent, having the least attraction for water-molecules, 

 would tend to usurp the position of the surface layer. Furthermore 

 the sohd phase, whether it be in the form of globules or in the continu- 

 ous element, would tend to increase and crowd together with a lessen- 

 ing of the more liquid phase. This would imply that when gelatine in 

 small proportion is mixed with agar or starch in the larger proportion 

 that the carbohydrate would form the colloidal framework or mesh as 

 well as the external layer of the mass.^ 



The separate colloidal masses where they do exist have, of course 

 definite boundary layers, as are formed wherever two colloidal phases 

 meet. Protoplasm may not be regarded, however, as altogether a 

 mechanical admixture of minute strands of material of different com- 

 position. Much of it, including the more fluid portions, must consist 

 of molecules of carbohydrates, proteins, salts, and even lipins aggre- 

 gated to form submicrons in the disperse phase or in the denser, more 

 sohd fibers, mesh, or honeycomb of the structure. The external layer 

 formed might well be in a sense a mosaic, but it is to be noted that no 

 actual proof of such a condition is at hand. Both absorption or imbibi- 

 tion and osmosis, including differentiated diffusions, would be affected 

 by the composition and relations of the two phases of the colloids in this 

 outer layer, and it seems highly probable that an adequate interpre- 



1 Free, E. E. A colloidal hypothesis of protoplasmic permeability. The Plant World, 21 : 

 141. 1918. 



