342 



THE AMERICAN NATURALIST [Vol. LI 



curring in living matter. This is because nuclear ma- 

 terial makes up a relatively small percentage of proto- 

 plasm, and because the reactions governed by enzymes 

 are ordinarily heterocatalytic. 



It is a remarkable fact that the chemistry of the cell- 

 nucleus has reached a stage of advancement superior to 

 that attained by the chemistry of the cytoplasm. It ap- 

 pears that the essential constituent of chromatin is a sub- 

 stance called nuclein, which is composed of a basic, pro- 

 tein factor and nucleic acid. The facts indicate that the 

 acid factor is the pennanent and essential component of 

 the nucleus, and organic chemical analysis seems to prove 

 that only one kind of nucleic acid exists in animal tissues, 

 although a different variety is to be found in the cells of 

 plants.''^ If, as now seems probable, the genetic enzymes 

 must be identified with the nucleic acids, we shall be 

 forced to suppose that these substances, although homo- 

 geneous—in animal or plant— from the point of view of 

 ordinary' chemical analysis, are actually built up in the 

 living chromatin, into highly differentiated colloidal, and 

 colloidal-molar, structures. The apparent homogeneity 

 results from the fact that ordinary chemical analysis pro- 

 vides us only with the statistics of the fundamental 

 radicles which are involved. 



To some minds, the idea that a portion of matter as 

 small as a germ-cell can contain sufficient catalytic sub- 

 stance to control the destinies of a complex organism, 

 seems hardly plausible. However, considering the slow- 

 ness of such processes as growth, it is clear that the quan- 

 tity of catalyzer required will usually be smaller than that 

 used in laboratory experiments; and it is a truism in 

 chemistry that radical alterations of reaction velocities 

 can be caused by the presence of almost infinitesimal 

 amounts of catalytic material.^*' From the nature of the 

 process, it is evident that only a few molecules of sub- 

 stance will be required to furnish the basis for an auto- 

 catalytic reaction which may eventually result in the pro- 



45 See Jones, W., "The Nucleic Acids," 1914. 



