CELLULAR ORGANIZATION OF LIVING MATTER 21 



from unrestricted diffusive interchange/ It is evident 

 that if a minute portion of protoplasm is to retain its 

 special chemical organization, it must be protected 

 against loss of its water-soluble constituents by diffusion, 

 and also against the unregulated entrance of soluble 

 substances from without. Chemical analysis shows 

 in fact that the crystalloidal content of living cells is 

 typically widely different from that of the surrounding 

 medium.^ The presence of a diffusion-proof partition 

 separating each small portion of living protoplasm from 

 its surroundings is apparently an essential feature of the 

 cellular organization. 



Without such a diffusion-hindering type of structure, 

 it is difficult to see how a high degree of chemical differ- 

 entiation could be maintained in such a system as the 

 living organism, consisting, as it does, in large part of 

 an aqueous solution of diffusible substances. Differences 

 in the distribution of soluble substances between proto- 

 plasm and surroundings would tend to equalize them- 

 selves by diffusion, and chemical differentiation would 

 become difficult or impossible. Morphological differ- 

 entiation has long been recognized as favored by the 

 subdivision of the developing germ into cells; this 

 condition permits morphogenetic processes in neighboring 

 cells and cell groups to proceed in relative independence 

 of one another.^ In a similar manner an essential 



^ Cf. my paper in Biological Bulletin, XVII (1909), 188, for a fuller 

 discussion. 



^ For a summary of work in this field, cf. Hober's Physikalische 

 Chemie der Zelle und der Gewebe (1914), pp. 370, 491; cf. also Bottazzi's 

 article in Winterstein's Handbuch der vergl. Physiol., I (191 1), 37. 



3 Cf. F. R. Lillie, "Adaptation in Cleavage," Woods Hole Biological 

 Lectures (1899), p. 43. 



