506 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in a fluorescence microscope, this means that as little as 10 -•s g. of fluores- cing material can be detected. SUMMARY Problems of cosmetic research and development are highly complex and extremely diverse in nature. It is not the intent of this article to suggest certain microscopic techniques for the solution of specific problems nor to discuss in detail the intricacies and accuracies of any one of the described techniques. On the contrary, the article tries to show, with the aid of a few selected specific problems, a general concept of a systematic approach which could usefully be applied to a multitude of different problems. In this approach, the first step will be only qualitative, i.e., an attempt to make the process accessible to direct microscopic observation. This will very often be possible, if not directly, then in the form of models or simulated sur- roundings. The result of this observation will normally be that the method is found unsatisfactory. Modification in general preparative techniques and selection of a more suitable optical method are the next steps. This is followed by specific adaptations of the preparative technique to the selected and appropriate optical method. Nothing is more revealing than a direct visual observation of "what happens," and one picture is worth not only a thousand words but, at least in the beginning, quite a few automatic sensing devices. This is particu- larly true in the study of dynamics, for example, by means of movies taken through the microscope. The first attempt at quantitative analysis can now be made, encompass- ing a survey of all available parameters and investigation of each one of them. No hesitation should be shown to create concepts or parameters which describe directly observable facts or phases of the process under study, even if they have to be expressed in terms which are not normally found in the scientific literature. It could well be that the process cannot or has not yet been described quantitatively in physico-chemical terms such as cm./sec. or mol./sec. Numerical values for these terms can normally be obtained only after the process has been understood. From these developed parameters, one indicating parameter should be selected which shows the highest coefficient of correlation to the examined effect, and this correlation should be confirmed. Actually, the indicating parameter may not always be the most obvious one. In all of these proceedings, it is advisable to use relative values only so that each experiment carries its own reference standards. This approach is much safer in a field where side effects may not have to be discovered and where the influence of systematic errors is not established. In many cases, relative values are all that may be of interest for the moment, and these may

QUANTITATIVE MICROSCOPY 507 be obtained by comparing the above secured values with those obtained in the same manner from preparations of different compositions or made by other manufacturers. A set of well-secured relative values can easily be connected to an absolute scale by one single calibration which, as a routine method, may be too difficult and time consuming to carry out. In the search for improved methods of observation and for indicating parameters, a surprising wealth o. information and techniques can be found in the literature, and often in the specialized literature published in totally unrelated fields. More often than not, such special techniques lend them- selves to easy adaptations. Very often, indicating parameters used in these fields of research can be applied to the cosmetic problem under study then it is especially advisable to use these known parameters. Their behavior, sensitivities to errors or changes, and range of validity have often been studied and described. Frequently, one will find all of the mathematics, which also apply to one's own problems, already developed. Cosmetic research with its highly diversified problems and demands for specialized knowledge seems to require even more imagination than research in any one particular field. Anybody actively engaged in research in this field will have to take advantage of every analytical method that might possibly be useful to him. Among these, quantitative microscopy plays an important role. (Received December 17, 1963) REFERENCES (1) T. Caspersson, Cell Growth and Cell Function, W. W. Norton and Co., lnc., New York 1950. (2) G. Oster and A. W. Pollister, Physical Techniques in Biological Research, Academic Press, Inc., New York, 1955. (3) M. L. Mendelsohn, 7. Bio•hys. Biochem. Cytol., 4, 407 (1958). (4) Rinne-Berek, in C. H. Claussen, A. Driesen and S. R6sch, .4nleitunge,l zu optischen Untersuchungen reit dem Polarisations-mikroskop, E. Schweizerbart, Stuttgart, 1953. (5) H. Ehrenberg, in H. Freund, Handbuch der Mikroskopie i,i der Technik, Vol. l, Part 2, Umschau-Verlag, Frankfurt, 1960, pp. 2- 186. (6) A. H. Bennet, H. Jupnik, H. Osterberg, and O. \¾. Richards, Trans. rim. Microscop. Soc., 65, 99 (1946). (7) H. Wolter, Schlieren, Phasenkontrast- u•d Lichtschnittverfahren, in S. Fliigge. Encyclo- pedia of Physics, Vol. XXIV, Springer-Verlag, Berlin, 1956, pp. 555-645. (8) E. Schuchardt, Das Integrationsverfahren in der mikroskopischen Tec•nik, in H. Freund, Handbuch der Mikroskopie in der Tech•ik, Vol. I, Part 1, Umschau-Verlag, Frankfurt, 1957, pp. 564-588. (.9) D. Hoenes, Mikroskopische Gru•dlage• der Technischen Gesteinskunde, in H. Freund, Handbuch der Mikroskopie in der Technik, Vol. IV, Part 1, Urnschau-Verlag, Frankfurt, 1955, pp. 362-378. (10) A. Thaer, Staub, 38, 555 (1954). Idem, Gliickauf, 91, 29 (1955). (11) J. Juda, K. Medenbach, Z. wiss. Mikroskop., 64, 218 (1959). (12) H. Osterberg and A. J. Carlan, Trans. •tm. Microscop. Soc., 77, 340, 353 (!958). (13) A. J. Hale, The Interference blicroscope, E. and S. Livingstone, Ltd., Edinburgh and Lon- don, 1958. (14) M. Fran•on, Interf•.rences, Diffraction et Polarisation, in S. Fliigge, Encyclopedia of Physics, Springer-Verlag, Berlin, 1956, pp. 171460.