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A digital software-controlled back-off system for probe lamp dc signal nullification has been designed and incorporated into a laser flash photolysis spectrometer. This method takes advantage of modern high-speed operational amplifiers already employed in the detection circuitry and the dedicated small computer that runs the spectrometer. The determination of I0, necessary for absorbance calculations, is inherent in the method.

Penetration of benzene through the skin of the rhesus monkey was determined using 14C-benzene, and quantitating the labelled metabolites in urine. The modes of application and amounts of benzene that penetrated the skin (indicated in parentheses) are as follows: (1) a single, direct cutaneous application of liquid benzene (0.172 +/- 0.139%); (2) a single application of benzene-containing [0.36%] solvent (0.0805 +/- 0.03060%); (3) multiple washes with full-strength benzene (0.848 +/- 0.0806%); (4) multiple washes with the benzene-containing [0.35%] solvent (0.431 +/- 0.258%); (5) removal of the stratum corneum followed by application of full-strength benzene (0.909 +/- 0.627%); and (6) application of benzene to the palmar surface (0.651 +/- 0.482%). Until more complete human data becomes available, benzene penetration in the monkey may be used to estimate penetration in man, both for industrial hygiene purposes and general toxicological use.

Percutaneous penetration of 14C hydrocortisone through normal vulvar skin (labia majora) was measured in six subjects and compared with that of the forearm. Of the topically applied hydrocortisone 7.7% penetrated vulvar skin whereas 1.3% penetrated forearm skin. This regional variation of percutaneous penetration may have toxicologic and therapeutic significance.