THE CELL AND PROTOPLASM 



initially quantitative in nature and which, 

 once established, constitutes a gradient in 

 rate of metabolic activity. Moreover, this 

 environmentally induced axial or meta- 

 bolic gradient then subtends the produc- 

 tion and transfer of active constituents 

 (chemical substances) in differentiating 

 cells and so predetermines the course of 

 later development. 



Factors of differentiation in later stages 

 of early development are discussed by Har- 

 rison as factors of the internal environ- 

 ment. These are illustrated especially from 

 his extensive transplantation experiments 

 on amphibian larvae. Here the develop- 

 mental pattern, which has progressed well 

 beyond the initial axiate stage of Child's 

 account, has demonstrably a primary cellu- 

 lar locus (organizer) in the region of the 

 dorsal lip of the blastopore, and later, vari- 

 ous secondary loci, which determine organ 

 differentiation throughout ensuing devel- 

 opment. Depending upon the age of donor 

 and of host as well as on the piece removed 

 and its disposition where transplanted, the 

 fate of the transplant and its effect upon 

 the organogeny of the host are strikingly 

 illustrated. From this it seems evident 

 that the fate and effect of a developing 

 part are functions of its relation to other 

 parts. This fundamental relationship ob- 

 viously marks the internal environment of 

 cellular differentiation. 



In the succeeding paper presented by 

 Kofoid, it is emphasized, however, that 

 even were the roles of both genetic and en- 

 vironmental factors of ontogenetic devel- 

 opment well understood, that knowledge, 

 essential as it must be, could constitute 

 only part of any adequate understanding 

 of the cell and organism. For the organ- 

 ism, beginning its individuality as a pri- 

 mordial cell, represents in its complete life 

 history not only the ontogeny that follows 

 its unicellular stage but also the phylogeny 

 preceding that stage. And all organisms 

 exhibit in this fundamental respect com- 

 parable life histories which may include, 

 even for numerous so-called unicellular 

 forms, a multicellular as well as a unicellu- 

 lar phase. Accordingly, it is only in terms 

 of their total life history as an expression 



of their evolutionary, developmental, and 

 environmental history that the cellular or- 

 ganization of living things can have basic 

 significance and the results of fundamental 

 investigations a satisfactory basis of inter- 

 pretation. 



The two papers that follow, one on 

 ''Chemical Aspects of Microorganisms" by 

 van Niel, and the other on "The Structure 

 of Viruses" by Stanley, mark a transition 

 from consideration of the cell and proto- 

 plasm of the more conspicuously cellular 

 organisms to a discussion of the subcellular 

 bacteria and of those ultramicroscopic, re- 

 producing entities, the viruses, whose sys- 

 tematic status, whether animate or inani- 

 mate, apparently remains a problem of 

 great moment. 



Recognizing Schwann's important con- 

 tribution not only to the formulation of the 

 Cell Theory but also to the concept of yeast 

 cells as vital agents of alcoholic fermenta- 

 tion, van Niel recounts the later develop- 

 ments of that concept, beginning especially 

 with Pasteur, which have now led to a dis- 

 tinctly basic and far-reaching generaliza- 

 tion. This generalization affirms that all 

 chemical activities of living organisms are 

 fundamentally hydrogen transfer reac- 

 tions. Postulated first by Wieland for 

 respiration, as essentially a dehydrogena- 

 tion of the respiratory substrate with oxy- 

 gen or some other agent as the final hydro- 

 gen acceptor, this concept has become ex- 

 panded by Kluyver and others to its 

 present broadest generalization. Thus all 

 enzyme activity in metabolic processes 

 serves primarily to facilitiate hydrogen 

 transfer reactions. And it now appears 

 that in the catabolic process this leads to 

 the formation of products from which the 

 building stones of cell growth and differen- 

 tiation are directly synthesized by means 

 of thermodynamically spontaneous reac- 

 tions. This comprehensive generalization 

 re-emphasizes the processes common to liv- 

 ing things as the fundamental processes, 

 whose elucidation provides our point of 

 departure for an adequate understanding 

 of the more complex vital phenomena. 



In this respect the succeeding discussion 

 on the viruses by Stanley is distinctly of 



