Growth and Colloidal Reactions. 5 



Available experiences with protoplasm lead to the conclusion that 

 it may be considered as a system of gels and sols in which the com- 

 ponent material is found in different conditions with respect to the pro- 

 portion of water combined or associated with it (see Chapter II). The 

 more fluid parts of the cell owe their liquidity to the fact that in such 

 material water containing a small proportion of the colloidal material 

 forms a medium or continuous element in which aggregations of mole- 

 cules or submicrons combined with a smaller proportion of water are 

 dispersed and may move about more or less freely. This condition 

 may be predicated of the contents of the vacuolar cavities and of the 

 regions in the cell which appear clear or vacant in living material or in 

 cytological preparations. The denser parts of the protoplast would 

 be composed of a much larger proportion of aggregated matter sepa- 

 rated by much thinner or more attenuated layers of the more fluid phase. 



Some writers assume that the submicrons of colloidal material aggre- 

 gate to form a continuous framework or structure which has been 

 hkened to a fine sponge, network of fibers, or honeycomb. The more 

 liquid colloid fills' the cavities or interstices of the framework. This 

 condition may not be so completely the reverse of the preceding as to 

 bring the more fluid colloid into complete discontinuity. It may be 

 safely assumed, in fact, that almost any mass of active protoplasm in- 

 cludes both conditions, and in a very fluid portion of the living inatter 

 small fragments of gel may be carried, while even in the denser newly 

 separated embryonic cell-regions minute cavities may be formed by 

 syneresis in which the colloid is in its extreme disperse condition. Such 

 syncretic cavities may well be the beginning of the vacuoles, in contra- 

 distinction to the view which assigns a definite morphological entity 

 to these features. 



The formation of these syneretic cavities, the size of the molecular 

 aggregates, and many other features of a colloidal mass are affected 

 by the dilution or dispersion of the original material, the rate of dehy- 

 dration arid gelation, and even such fundamental characters as the 

 relations of the two phases may be affected by the origin and rate of 

 deposition of the material. In addition to these very fertile sources 

 of variations in living matter, the cell at most times carries inclusions, 

 such as starch grains, crystals, and protein granules which are com- 

 paratively inert, partly by reason of their small surfaces, and may not 

 exercise much influence upon the surrounding gel. Oxidation, proteo- 

 lysis, hydrolysis, or solution of these bodies may set free or split the 

 compounds included, and these, quickly diffusing through the colloidal 

 mass, may play an important part in the morphological crises of the cell. 



Many mistaken attempts have been made to compare the growth of 

 organisms and the formation of crystals directly, and to establish their 

 identity or continuity. The results of such efforts serve to bemuse the 

 mystic, to divert the philosopher, and to furnish poetical conceptions 



