In a previous paper ( '32) we reported that with the effect of genetic constitution eliminated, the concentration of sulfhydryl, -SH, in newly born rabbits is related to the intensity of metabolic processes. This conclusion was drawn because in the whole carcass of newly born rabbits of the New Zealand Red breed, nursed f o r 48 hours, the mean concentration found was 64.6 2 1.42. The mean concentration of the non-nursed litter mates, fasted 48 hours, was found to be but 33.9 1.08.
The sulfhydryl estimation, as reported in this ( '32) and subsequent papers ( '33 a, '33 b, '33 c), was made from the iodinereducing power of tungstic acid filtrates prepared from water extracts of the entire carcass after grinding with sand. Results were expressed in terms of glutathione, the principal sulfhydryl compound present. We recognized that any ascorbic acid present would be oxidized by iodine and included in the sulfhydryl estimation. Since the publication of this report, Birch and Dann ('33) have shown that determinations of glutathione in tissue extracts by means of the iodine titration gave too high results, because the tissues contained ascorbic acid that was also oxidized by the iodine. These authors employed a modified method of Tillmans ( '30) for estimating ascorbic acid, using 2,6-dichlorophenolindophenol as an oxidizing agent. According to their findings, the ascorbic acid fraction accounted for as much as 40 per lThis investigation was aided by a grant from the National Research Council for the study of glutathione in relation to growth and hereditary size.