Phenocopy and Norm of Reaction 261 



process through which the mutant works may or may not be the same 

 as in the phenocopy. In Landauer's work the primary process in the 

 phenocopy of rumplessness, and so on, after the treatment of the 

 embryo with insuhn, pilocarpin, and boric acid, was clearly an inter- 

 ference with carbohydrate metabolism. It would be wrong, however, 

 to demand that the mutant works also by interference with this phase 

 of metabolism, but this does not mean that in a given case both 

 primary actions might not be the same. This problem would have to 

 be decided from case to case, though it might be safe to say that 

 phenocopies produced the same way by radiations, temperature 

 shocks, and chemicals will not belong to this category, but rather 

 work by means of the kinetics controlled by the primary action, 

 whatever this is. 



If we keep this in mind, the further exploration of the chemical 

 situation in such cases as Landauer's will be very interesting. It is 

 an important fact that substances like insulin, sulfanilamide, eserine, 

 boric acid, and pilocarpin produce many similarities in their over-all 

 effects, though there are dissimilarities in details of expression. In all 

 these cases, nicotinamide serves as a protective supplement, thus 

 pointing to a common biochemical basis for the activity of these 

 compounds, though the grade of "protection" is different with differ- 

 ent compounds. Now it turned out that the skeletal abnormalities 

 produced by boric acid are very similar to those known for riboflavin 

 deficiencies. Thus the hypothesis is made that the effects are mediated 

 by means of riboflavin-containing enzymes. Chemical data (see Lan- 

 dauer, 1952a ) on the action of boric acid on riboflavin-containing mol- 

 ecules agree with such conclusions. "It is well known that one of the 

 fundamental purposes of the riboflavin enzymes is to serve as 'bridges' 

 over which the hydrogen atoms accumulating on the nicotinic acid 

 coenzymes can be passed to systems which will carry out the reduc- 

 tion of oxygen" (quoted from Williams by Landauer). According to 

 Landauer, these neighboring functions of nicotinamide and riboflavin 

 enzymes in carbohydrate utilization, and their disruption by insulin 

 and boric acid, respectively, presumably explain that allied yet 

 separate teratogenic results are produced in the two instances. With- 

 out going into further details, it is obvious that this type of analysis of 

 phenocopies (which many of these teratogenic effects are) can lead 

 to important insight into the biochemical control of growth processes. 

 Applied to favorable material, it might one day also permit conclusions 

 upon the primary effect of mutants, which are phenocopied. 



Thus it is highly probable that the view is correct which considers 



