Thus was established a reaction series of the kind we had originally con- 

 ceived. Substituting the known chemical, it is as follows: 



H H 



I I 



-C— C— COOH 



I I 

 H NHj Tryptophan 



/ 



O H H 



il I I 

 -C— C— C— COOH 



yCVfCt N-Formylkynurenine 



NH 



H H 



I ! i 



-C— C— C— COOH 



I i 

 H NH2 



Kynurenine 



NH, 



en 



O H H 



II I I 

 — C— C— C — COON 



I 1 

 H NH 



04 H.. 



3-hydroxykynurenine 



OH 1 



Brown Pigment 



A Neiv Approach. 



Isolating the eye-pigment precursors of Drosophila was a slow and dis- 

 couraging job. Tatum and I realized this was likely to be so in most cases of 

 attempting to identify the chemical disturbances underlying inherited ab- 

 normalities; it would be no more than good fortune if any particular example 

 chosen for investigation should prove to be simple chemically. Alcaptonuria 

 was such a happy choice for Garrod, for the chemistry had been largely 



s-33 



