262 Heredity and Eugenics 



or to remove the by-products which would inhibit the 

 katalyzing action which would normally go on. Under 

 the modified conditions there may be produced no greater 

 alteration in the germ than a reversed action of some 

 enz}'me, and although the same enzyme may be present, 

 its reversed action is such that the pigment-forming sub- 

 stance is not formed, but its activity is directed to other 

 activities than to building pigment-forming substances. 

 The same enzyme may again be reversed in its direction 

 either by combining with some other substance, or by being 

 acted upon by some incident force, and this reversal of action 

 in the enzyme may therefore produce the formation of 

 color substances. It does not of necessity follow that the 

 changes induced are at all concerned with the substances 

 which actually themselves form the pigment. For example, 

 in germinal modifications which have been produced, where 

 the color is diminished in intensity, there may be identical 

 amounts of chromogen and enzyme, but the changes may be 

 due to changes in other factors which are necessary to the 

 color formation by removing from the field of operation 

 certain inhibiting by-products. 



It is possible that a profitable point of attack upon these 

 problems lies in this direction. The chief difficulty, however, 

 is the small size of most germ cells, and in those of large 

 size the existence in the egg of a large amount of stored 

 food supply effectually inhibits investigation. It is prob- 

 able that for the present interpretation of the process of 

 germinal change must be more by analogy than by actual 

 physical and chemical analysis. 



In the experimental production of modifications of the 

 germ plasm two definite ideas as to the nature of the change 

 have been expressed. MacDougal is of the opinion that 



