Biological NJfrogen Fixation 115 



fixation — agents hitherto unsuspected of this valuable 

 characteristic (4, 6, 9, 12, 17). 



But in leaving this second case history, once again note 

 that the apparatus used was one that was practically dic- 

 tated by the fashion of the period, and certainly something 

 like it would have been constructed by anyone embarking 

 on the proposed study. But such a method inevitably led 

 to use of hydrogen as an ''inert" gas, and once this choice 

 was made, the discovery of its inhibitory action was only 

 a matter of time. Had we originally employed the more 

 sensitive microrespirometer technique, this finding might 

 have been overlooked, as it certainly was by the investi- 

 gators using that technique at that time (2). 



Case History III, Chemical Infermediafes by 

 I so to pic Tracing 



The year 1939 marked the end of an era in the research 

 on the chemical and enzymatic pathways in biological 

 nitrogen fixation. By this time exploitation with the two 

 major tools that had been employed so assiduously during 

 the past decade had just about reached the point of di- 

 minishing returns. At a meeting of the Third Commission 

 of the International Society of Soil Science held at New 

 Brunswick in early September, representatives of the two 

 schools summarized once more the chief findings revealed 

 by application of the two methods (14, 19) and then en- 

 gaged in a rather pointless and futile argument as to which 

 approach — the "organic chemical" one of Helsinki or the 

 "physical chemical" one of Madison — would be the more 

 powerful for new revelations. 



The beginning of World War II within a few days all but 

 stopped research in this field. By the time full-scale experi- 

 mentation was resumed in the late 1940's, powerful new 

 techniques resulting directly or indirectly from the acceler- 

 ated research of the war period were available for applica- 



