776 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Derartige Ver'&qderungen laufen nicht innerhalb von Mmuten oder Stunden nach der Herstellung ab, sondern nehmen Wochen in Anspruch. Der unmittelbar nach der Herstellung gegebene gute Schutz gegen mikrobielle Kontamination ist zum Zeitpunkt des Verbrauchs darm nicht mehr gegeben. Bei Verkeimung setzt ungehemmtes Keimwachstum ein. Die oben angedeutete Abh'&ngigkeit der Verteilung der teilweise wasserRJslichen Parabene yon der Rezeptur und ihren Variationen und damit synchron zu beobachtende 'Anderungen der mikrobiellen Belast- barkeit belegen die Bedeutung derartiger Untersuchungen. Sie gestatten, den Grund ffir Unterschiede in der Belastbarkeit zu finden und die Optimierung der Konservierung emes Priiparates zu steuern. Bei fehlender zeitlicher Ver'•ndemngen yon Konservierungsmittelgehalt und -verteilung kann man fiber die mikrobielle Belastbarkeit die Aussage treffen, dag die Ergebnisse der einmalig durchgeffihrten, mikrobiologischen Unter- suchung weiterhin gfiltig sind. Zusammen[assung Dutch Ultrafiltration und Ultrazentrifugation ist aus Emulsionen die kontinuierliche Phase ohne merkliche 'Anderungen hinsichtlich Ver- teilungsgleichgewichten und Adsorptionscharakteristik zu gewinnen. Die Analyse per HPLC erm6glicht die quantitative Bestimmung der in der kontinuierlichen Phase enthaltenen Konservierungsmittel. Diese Daten korrelieren gut mit den Resultaten des mikrobiologischen Be- lastungstests. Herin Dfising danken wir ffir die Durch 'ftihrung einiger Untersuchungen, Fr. Dr. Kran ffir die mikrobiologischen Daten. Literatur [ 1 } Handbuch zur Ultrafiltration, Fa. Millipore/Neu-Isenburg. [2} Applikationsbeispiele der Fa. Waters, K/Smgstein. 13J Wilson, C. H., J. Soc. Cos. Chem. 25, S. 67-71 {1974}. [4} Marszal, L., Zbl. Pharm. 113 [1974} Heft 9.

j. $oc. Cosmet. Chem., 29, 777-782 (December 1978) Effects of harvesting techniques on hydration dynamics: gravimetric studies of stratum corneum ROBERT L. RIETSCHEL and WILLIAM A. AKERS Department of Dermatology Research, Letterman Army Institute of Research, Presidio of San Francisco, CA 94129. Received October I I, 1977. Synopsis STRATUM CORNEUM specimens HARVESTED by several methods commonly used for in vitro studies have been compared by HYGROSCOPICITY. Cantharidin blisters give superior data when compared to heat, trypsin and ammonia fume separated specimens. As the cantharidin data represent skin from a different age group and body site, a comparison to animal and human data in the literature is made. INTRODUCTION Many experiments have been done using isolated sheets of stratum corneum. In 1963, Kligman and Christophers reported three techniques for preparation of these sheets: 1) exposure to ammonia fumes for 30 min in a closed vessel over concentrated ammo- nium hydroxide, 2) heat separation by immersing skin sandwiched between metal plates in a water bath at 56øC for 2 min followed by the removal of the epidermis, which is floated overnight in a buffered 0.0001% solution of trypsin and 3) in- traepidermal blistering with a 0.2% cantharidin solution occluded for 8-10 hr (1). They claimed that stratum corneum prepared by canthardin and heat methods was the same with respect to water diffusion and stress-strain characteristics, but no data was presented. Onken and Moyer obtained stratum corneum by digesting skin samples for 24 hr in 3% trypsin (2). Proteolytic enzymes other than trypsin have been used. Kligman and Christophers used papain, pepsin, ticin and elastase, but found them less effective than trypsin. Pronase is also useful (3). Middleton used 2M urea with 0.5% trypsin to obtain guinea pig foot-pad corneum which he compared with foot pad removed at 60øC for 30 min (4). He found no difference in the water binding ability of guinea pig foot pad prepared in these two ways. Another popular technique requires immersing skin in 2M sodium bromide for 2 hr at 37øC (5). Stretching has also been employed (6). Marzulli uses tape stripping of stratum corneum eluted with organic solvents (7). Each technique has its limitations. Some can only be utilized on excised skin. Several methods employ prolonged water immersion. The effects of enzymes on epidermal 777