INDIRECT COOLRIMETRIC ESTIMATION OF CYSTEINE 311 acetone and the solution is made up to 100 ml. with distilled water. The solution thus obtained shows a slight coloration but can be used without further purification. /lpparatus The extinctions were measured with a Beckman DU spectrophotometer provided with a photomultiplier. The cell used had a 10 mm. light path and the slit width chosen was the one giving the maximum sensitivity. The pH values indicated in the text were taken with a Beckman G. apparatus. Procedure 1 mi. of ferricyanide solution is measured into a 100 mi. volumetric flask 20 mi. of distilled water are added, followed by the solution of cysteine to be determined. To ensure a complete reaction between cysteine and ferricyanide, the mixture was allowed to stand for five to ten minutes. Then 0.5 mi. of ZnSO4 solution and finally 0.5 mi. of (freshly prepared) aqueous solution of 0-dianisidine is added and the volume is made up to 100 mi. with distilled water. Readings are taken at 470 mt• after ten and thirty minutes standing. When a series of assays are made adding 10 mi. of the cystine solution simultaneously with the cysteine solution the results obtained for the extinctions are identical with those previously obtained. CONCLUSION 1. A new indirect colorimetric method for determination of cysteine is presented the method is based on the reducing action of cysteine on an excess of ferricyanide ion after which this excess is estimated using 0-diani- sidine. 2. For the cysteine concentrations considered, no perceptible variations of extinction values of the obtained colors have been observed even when large amounts of cystine were present reaching as much as 50 times cys- teine concentrations. 3. Extinction values remain constant during the interval of five to thirty minutes after the 0-dianisidine reagent has been added. 4. Beer's law remains valid up to minimal cysteine concentrations of 0.6 tzgm./ml. corresponding to a 1:1,700,000 dilution limit. A new indirect colorimetric method for cysteine determination is de- scribed. The method depends on the oxidation of cysteine in alkaline solution using a known excess of ferricyanide, the latter being determined by the extinction at 470 m• of the colored solution produced by adding 0-dianisidine to the mixture previously acidified at pH 1.5-2. The

312 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS proposed method allows a quick and easy estimation of cysteine in solutions containing amounts as little as 0.3 •gm./ml. The presence of cystine even in concentrations reaching 50 times those of cysteine does not interfere with the procedure. REFERENCES (1) Artigas, J., Buscar6ns, F., and Rodriguez-Roda, C., Alnles real soc. espah. f4s. y qufm. (Madrid), 56-B, 377-8 (1960). (2) Vassel, B., )e. Biol. Chem., 140, 323 (1940). (3) Nakamura, K. and Binkley, F., [bid., 173, 407 (1948). (4) Mentzer, C., •. pharm. chim., 27, 145 (1938). (5) Hazeloop, E., Chimie & inustrie, 33, 325 (1935). (6) Sch6berl, A., Ber., 70B, 1422 (1937). (7) Hellerman, L., •. Arm. Chem. Soc., 63, 2551 (1941). (8) Barnstein, H. D., •. Biol. Chem., 89, 125 (1930). (9) Kolthoff, I. M., and Stricks, W., Atril. C,•em., 26, 366 (1954). (10) Kolthoff, I. M., and Stricks, W., [bicl., 23, 763 (1951). (11) Kolthoff, I. M., and Stricks, W., •. Aim. Chem. Soc., 72, 1952 (1950). (12) Buscar6ns, F. and Artigas, J., Atril. Chim. Atcta, 19, 4343 (1958). (13) Buscar6ns, F. and Artigas, J., [bid., 16, 452 (1957). (14) Artigas, J., Buscardns, F., and Rodriguez-Roda, C.,/lnles real soc. espa•. fis. y qufm. (Madrid), 56-B, 369 (1960). (15) Artigas, J., Buscar6ns, F., and Rodriguez-Roda, C., [3id., 56-B, 373 (1960). EFFECT OF VARIOUS METALLIC IONS ON THE GROWTH O F Penicillium glaucum, Aspergillus niger and Achorion quinckeanum By R. BP. trN and A. MAGGIORA* Presenled at the Conference InternationaL' de la Soci4td Suisse des Chimistes Cosmeticiens, Genbve, /lugust 26-28, Iv •T •s true that the growing of micro6rganisms is dependent on the presence of metal ion traces, it is no less certain th_•t some cations in a specific concentration have the opposite effect. Of the latter, silver is the best known and its antiseptic effect has been used prof- itably for quite a long time. Nowadays in spite of the synthetic disin- fectants and antibiotics, the antiseptic properties of the silver salts are still used. The process of inhibition by metals has been studied mainly on the growth of bacteria, and on Staph. aureus in particular in particular. Here related researches result from several observations. First: when observing the growth of .4chorion quinckeanum on pieces of guinea pig * Depart. of Dermatology (Chairman: Prof. W. Jadassohn), University of Geneva, HSpital Cantonal• Geneva, Switzerland.