28G 



THE AM KlUC AX NATURALIST 



[Vol. XLV 



to the same fundamental laws of chemical behavior 

 whether they exist in living matter or in non-living 

 matter. If in the comparatively simple cases of associ- 

 ated simultaneous reactions with which we are acquainted 

 in non-living matter, relative velocities may so modify 

 the results, we can readily realize of what tremendous 

 importance regulation of this matter must become in 

 living protoplasm where doubtless vast numbers of 

 chemical reactions and interactions are going on at the 

 same time. In fact, could we locate such a time regula- 

 ting factor in the germ-cell it would seem that we had 

 accomplished a long stride toward an understanding of 

 the controling and coordinating mechanism which in- 

 sures the appearance of just the proper substance at the 

 right time in morphogenesis. It would constitute a quali- 

 tative as well as a quantitative regulator, for by deter- 

 mining quantity at any given time it determines what the 

 next chemical reaction will be, and hence in the very doing 

 of this, it necessarily conditions the chemical outcome of 

 that reaction. As we have seen, temperature and cata- 

 lytic agents are important factors in modifying the velo- 

 cities of reactions in ordinary chemical processes, and 

 inasmuch as under normal conditions of development the 

 temperature factor is a fairly constant one, we are left 

 to face the question as to whether in protoplasmic phe- 

 nomena there is anything to correspond to catalyzers. 

 Such substances we find in the enzymes. 



While the method of enzyme activity is not positively 

 known, the consensus of opinion of those who have 

 studied them most seems to be that they act by catalysis. 

 For instance, both catalyzers and enzymes are effective 

 in very minute quantities; neither appears among the 

 end-products of the substances acted upon, but exists in- 

 dependently and in exactly the same quantity as at the 

 beginning of the reaction; external conditions such as 

 temperature affect their activities similarly; and lastly, 

 the rate, that is, the velocity of the reaction concerned, 

 depends upon the amount of the catalyzer or enzyme 

 present. When we have explained the phenomena of 



