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

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



H H 



C— C—COOH 



i i 

 H NH 2 Tryptophan 



I ' 



O H H 



II I I 



-— C— C— C— COOH 



H NH 



s/ 



CHO 

 NH 



I 



O H H 



II I I 

 — C— C— C— COOH 



N-Formylkynurenine 



I I 

 H NH, 



Kynurenine 



NH, 



en 



O H H 



II I I 

 -C — C — C — COON 



I I 



H NH, ,, . 



3-hydroxykynurenme 



OH 



Brown Pigment 



A New 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-81 



