324 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS containing proteins present in the hair (such as cystine and cysteine) and the silver salts in the photographic emulsion. The adsorption of sulfur 35 tagged dyes and the penetration of hair fibers by sodium bromide (tagged with bromine-82) has also been thoroughly in- vestigated (6). Studies of this type are of interest in cosmetic chemistry since much can be learned of the additives used in preparation of hair dyes and rinses. In respect to skin studies, the literature contains many articles which de- scribe the use of radioisotopes as tools for the evaluation of materials on both human and animal skin. In most instances, radioisotopes were used because there was no alternate method of obtaining the answers desired. Since attempts to extrapolate in vitro or test tube results in terms of what would occur in the presence of living cells often results in failure, studies were undertaken directly on living tissue. Numerous studies have been undertaken on the skin adsorption of carbon-14 tagged bacteriostats. Studies have been performed in respect to the adsorption of hexachlorophene from soaps onto the skins of rats, rabbits and humans (7, 8, 9, 10). The effect of repeated washing of living skin with soaps containing the tagged bacteriostat was investigated, and build-up of the bacteriostat was followed. Also studied was the effect of concentration of bacteriostat on build-up as well as the rate of removal of the compound from skin tissue by washing with soap containing no bacteriostat. Figures 3, 4 and 5 pictorially show how this type of study was conducted on animal skin. These pictures, taken during an actual experiment show --'."• t.,,..•.• •:•:?,,,4•,,•. •,'&:•'•,t• ff•"•'• •t}• :'. :.7..,• --- . .... : •--' • -q.•.: ...... .'•--. ... • •: .•.• :.•... - .. • ..... - .a?½ '•. •. .•: ß • •.. •._. .... .r:...:.: ß '2•!•5- '.-.7 :.. ß • ':'.'¾)?,' .3• % L:-':' ' .•.g.. ....• L-• -.. %. :.:A.,•:.L..3::...•:•. ... ............... ...'... ................ •.•.. "" ' " ß . . ....... .... ...•,...e• ........ . ,.•:5•.. ........ ::..: -.• ..... :.... ......... : ":' --•i•7'•:•.•4:• .":'•i5•5Z"•..•::::•.':• :'.::5•+,= ::• .: ".'7.':"::: Figure 3.

RADIOISOTOPES IN DETERGENT AND COSMETIC RESEARCH 325 stepwise the procedure used. Figure 3 shows the shaved skin of the rabbit. The section on the upper back was generally used as the test site since a reasonably flat area could be found on which to position the special radio- assay device. The actual assay site on the rabbit skin was marked with India Ink. Figure 4 illustrates the washing of the skin with the soap con- taining the tagged bacteriostat using a small section of a cellulose sponge (used since it adsorbed little or no bacteriostat). After the skin was rinsed with water and dried with a hair dryer, radioassay was undertaken as shown in Fig. 5 using the special "Flowgas Cell" devised for this purpose. Figure 6 shows a closeup of this cell which has been described previously in the literature (7). The cell is advantageous over a thin and window Geiger- Mueller tube in that it possesses much greater sensitivity. Furthermore, since it is placed in intimate contact with an adsorbing substrate such as skin, the distance from detector to radioactive source is fixed and geo- metrical corrections are not necessary. In all cases normal chemical analysis of the bacteriostat, even in vitro, was difficult, sensitivity was poor and many other compounds interfered with the analytical procedure. However, with radiotracer techniques, adsorption values were easily obtained. The adsorption and retention of carbon-14 tagged emollients from lotion formulations by human and animal skin has also been studied (5, 11, 12). In some cases special radioassay devices were designed in order that proper experimental procedure was used and that results obtained were valid. Cold cream labeled with carbon-14 has also been used in studies and has been found to penetrate only very slightly into the skin (12). Evaluation of astringents used as antiperspirants in lotions and sprays Figure 4.