THE CATALYST ENTELECHY IN DIFFERENTIATION 197 



area has essentially the reverse electronic impression on its near 

 side, but a duplicate impression on its off side. If on leaving the 

 molding surface the plaque is adsorbed by some other surface 

 (which may be a particulate carrier) in such manner that its off 

 side faces the milieu, we may have a workable duplication of the 

 original catalyst area. (Adsorption the other way round may 

 lead to antibody formation). 



This notion of new self-duplicating catalysts does not gainsay 

 the dominating importance of the chromosomes and genes, but 

 it does indicate how even one single molecule could serve to estab- 

 lish the catalytic formation of new substances in a cell clone. In 

 fact it has been reported 33 that one crocin molecule is able to in- 

 duce a sexual change in an alga. The position of the gene is 

 sufficiently secure to permit even the most devoted followers of 

 T. H. Morgan to admit the existence of non-genic heredity of 

 the catalyst type; or they may prefer to consider a new auto- 

 catalytic catalyst as a symbiont or an extrachromosomal gene. 



Let us now consider some of the experimental evidence indi- 

 cating that cells are able to form new and heritable catalysts. 



Apart from the many specific catalysts known to exist in yeasts, it has 

 long been known that yeast can be "trained" to ferment certain sugars. 

 Nearly half a century ago F. Dienert 34 found that a yeast which was 

 unable to ferment galactose acquired this power when small but con- 

 tinually increasing percentages of this sugar were added to the fer- 

 mentation mixture. 



Karstrom 35 divided the enzymes of microorganisms into two groups: 



(1) constitutive enzymes, whose formation is common to all media; 



(2) adaptive enzymes, which are formed only if the cell is "stimulated 

 by the presence of a specific chemical substance in the milieu," a pro- 

 cedure which recalls the formation of antibodies in animals as a 

 response to an antigen. On experimenting with nine strains of yeast 

 (Saccharomyces), H. E. Rhoades 36 found that each strain could ferment 

 glucose, mannose, sucrose and raffinose regardless of the carbon source 

 in which the cells had grown; that is, these sugars were fermented by 

 constituent enzymes. On the other hand, maltose, trehalose, alpha- 

 methylglucoside and galactose* were fermented only if the organism 

 had been "trained" by growth in the presence of the specific substrate 

 or a closely related substance, that is, after the formation of adaptive 

 enzymes. 



Evidently, yeast can "manufacture" new enzymes to meet new 



* One strain (S. cerevisiae Hansen) possessed the inherent ability to ferment 

 galactose. 



