372 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS CO2formed was trapped in phenethylamine solution* and counted using standard procedures. The averages for each set of samples (in micro- curies) were plotted against the observed surface counts. The relation- ship between surface counts and total radioactivity in and on the skin is shown in Fig. 1. 48 • 40 eo • S2 0 24 0 5 10 15 20 25 Surface Counts x iO-3/Min. Figure 1. Relationship between surface count and radioactive content of skin * This solution consists of 27% v/v absolute methanol, 27% v/v 2-phenethylamine, 0.5% w/v PPO (2,5-diphenyloxazole), and 0.91% w/v POPOP [p-bis-2-(5-phenyloxazolyl)benzene] and toluene, q.s. to 100%. ,' i The average counting efficiency for the recovery of radioactivity ap- plied to skin using the Schoeniger combustion technique was 56.2%. This efficiency was determined by burning samples of skin to which known quantities of radioactivity had been applied. For the human study, five adult male and five adult female subjects were employed. The subjects were instructed to adhere to their usual habits in washing their hands using a control bar soap identical with that which was supplemented with bacteriostats when the antibacterial soap solutions were prepared. The use of hand creams, lotions, or other prep- arations was not permitted during the experimental periods.

ANTIBACTERIAL AGENTS IN HUMAN SKIN 373 The appropriate test formulation (0.1 ml) was applied once each morning for 5 consecutive days to the dorsal surface of the left hand of each subject on an area measuring 3.5 cm in diameter. The method of application was as described for the animal studies. Excess material was rinsed off with tap water 3 min after application. The surface skin counts were determined immediately and 15 min, 4 hours, and 24 hours after each application of the test material. No washing of the test sites was allowed for 4 hours following application of the test material. Applications were made daily for 5 days. Relationship of Surface Counts to Total Radioactivity in and on the Shin The activity (in microcuries) in and on the skin of each subject treated with the labeled soap suspension was determined by counting the surface of the skin using a Nuclear Radiation Detector and converting surface counts to total activity using the graph (Fig. 1) constructed from data obtained in the animal studies, and assuming analogy between human skin and rat skin. RESULTS Elficiency of Surface Counting From Fig. 1, a surface count of 30,000 cpm is equivalent to 0.0565 vc/cm 2 of skin. If all of the radioactivity were on the surface and if counting were 100% efficient, the detectable surface counts may be cal- culated using the following conversion formula: cpm a •c X 2.22 X 1060 6.06 c 1.33 a 0.0565 X 2.22 X 106 X 6.06 cpm = 1.33 cpm = 5.72 X 105 of radioactivity in and on the skin detectable by surface counting (% efficiency) 30 X 10 • 5.72 X 105 X 100 = 5.25 a Does not include a background of 65 cpm. b 1 /•c = 2.22 X 10 • disintegrations per min. * The effective surface area of the Nuclear Radiation Detector used was 6.06 cm 2. a 1.33 is an aliquot adjustment. After combustion of a skin sample, the carbon dioxide formed was collected in 20 ml of basic scintil]ator solution and 15 ml of the solution was counted in a liquid scintillat,•on counter.