PHYSICO-CHEMICAL ASPECTS II 



bable that the substances which have just been men- 

 tioned are essential constituents of genes: in fact it is likely 

 that a gene can be considered as a special array of en- 

 zyme molecules, organised so as to produce one chemi- 

 cal product, or a small family of chemical products. The 

 substances so produced are those involved in the medi- 

 ation of the effect of the gene. In addition to these sub- 

 stances, the gene has the capacity to reproduce itself 

 completely. The extent to which this is a different func- 

 tion from that of producing the substance or substances 

 concerned in the mediation of the genetic effect is un- 

 known. 



The sharp localisation of chemical substances in the 

 chromomeres, and the variation in concentration of 

 these different substances from chromomere to chromo- 

 mere, must involve also, through the operation of Don- 

 nan equilibria etc., highly local variations in pH along 

 the chromosome and probably also in the SH content 

 of different parts of the chromosome. These two phy- 

 sico-chemical factors must be very important to consi- 

 der in relation to the enzymic activity of a gene. 



Physico-Chemical Aspects 



The foregoing discussion has been based mainly on 

 consideration of the cytochemical distribution of diffe- 

 rent substances. In forming a picture of the physico- 

 chemical system characteristic of the cell, we must con- 





