The metabolism of the trichloronitrobenzenes in the rabbit.

reaction may be more readily standardized because the time ofheating is not so critical as in the method of Thomas. Further, the time of heating is sufficiently long to allow equilibration between the boiling-water bath and the content ofthe test tubes, so that differences in wall thickness are not important. It is also unnecessary, since the colour is stable, to take readings within 8 min. of completion of the reaction. The reaction is thus easier to handle and more reproducible than the earlier method. The present method is also preferable to that of Udenfriend & Cooper (1952) since it avoids extraction ofthe excess ofnitrosonaphthol by ethylene dichloride. Recoveries also seem to be more complete by our method. As far as specificity is concerned our method does not differ from those of Thomas (1944), Giral (1944) and Udenfriend & Cooper (1952). The only compound which could seriously interfere appears to be tyramine, which is commonly absent from protein hydrolysates. SUMMARY