EVALUATION OF CHEMICALS TO ANIMAL SKIN 183 texture, color and sheen. However, this is still only a guidepost to human reactions since animal skin is normally much more constant in appearance than the human skin. Certainly the application of a cosmetic formulation to the soft, smooth pink skin of the freshly clipped rabbit gives one no real idea of what that same formulation might do on the sun-tanned, wind- roughened facial skin of the human being. Certain cosmetic properties can be evaluated under these same sets of circumstances. For example although the rabbit skin is deficient in melanin and does not tan under excessive exposure to ultraviolet light, it does react with edema and erythema and hence it can be used for comparing the efficacy of sunscreen candidates. Such a screening program is purely mechanical, however, and would not give one a clear-cut insight into ease, degree, and color of suntan to be achieved in the human with such a candidate compound. This is an example of carefully delineating the objective, knowing the possibilities and limitations of the animal experimentation, and exploiting the method to its fullest without being misled by its eventual application. To the extent that cosmetic effects include the healing of superficial cuts, scrapes, and abrasions, these properties can be evaluated in animal skins under controlled conditions. Keratin staining and discoloration can be evaluated, as can the degree of roughening or sloughing under con- ditions of repeated application. These, then, do give us some examples of evaluation of the cosmetic effects, but certainly the final answer must come from the eventual user of the cosmetic and not from the rabbit. As is frequently pointed out, methodology is the big void in our present approach, not only to animal but to human evaluation of skin reaction. More adequate methods of evaluating vascularity, color, smoothness, reflection or gloss, pH and even chemical composition of the superficial layers are obviously necessary. The use of radioisotopes is one new method which is beginning to find application. This method may eventually find its proper place in the cosmetic evaluation scheme. I should like to caution, however, against overenthusiasm for it in the cosmetic field, lest we not profit from the experiences in the related fields of biochemistry, pharma- cology and therapeutics. The technical traps are many and dangerous and perhaps the greatest of these problems is that of interpretation. I am sure there are those attending the seminar who are more qualified to discuss this subject than I am, though I mention it here primarily to be sure that it is included in the discussion agenda. It is probable that, as radioisotope techniques develop, animals will play a very important part in the ap- plication. In summarizing the applications of animal testing of chemicals, I should like to emphasize that, whether the test subject be animal or human, the test can be no better than the team of investigators conducting it. strongly feel that the chemical evaluation from the cosmetic standpoint is

184 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS essentially a teamwork proposition involving cosmetic chemists, pharma- cologists, and dermatologists. The most important aspect is a careful delineation of the objective which is being sought and a recognition of the limitations of whatever methods are being applied, whether to animals or to humans. Certainly most species have their place in the over-all program. We strongly recommend the use of animals for all of the preliminary screening and evaluation phases. This applies to irritation, sensitization and preliminary cosmetic aspects. To do otherwise poses an unnecessary hazard to the human test subject and severely limits the scope and volume of the screening which can be completed. In effect, our view is to know the advantages and limitations of each group of subjects and to use the animal wherever the use is practical, since if the cosmetic industry is to make the advances which the progress of chemistry has made available to it, both animal and human resources must be used to the ultimate maximum capacity. There is much work to be done with each species, and each has its place in the over-all program. TOWARD EMULSION CONTROL* By SYr)•E¾ Ross Rensselaer Polytechnic Institute, Troy, N.Y. ONLY WHEN THE control of any physical process is assured, when we are aware at all times of what is taking place, and can alter it at will, can we derive maximum utility from its application. In the field of emulsion technology we can report progress but we are still far from this ultimate goal. I propose to review briefly for you the methods that we can now summon to help us learn what is taking place during the formation and subsequent aging of emulsions. This is still only half the story, but we certainly cannot go on to effect alterations at will unless we first know the situation. A grand step forward in the control of emulsion formation was the recog- nition by Bancroft that the continuous medium will be the one in which the stabilizing agent is more soluble. This rule has recently been made quantitative by Griffin, with the introduction of the HLB system of choosing emulsifying agents (1). The very first question, that of emulsion type, is thus brought under control. There are still left many other pos- sible variables. The nature of the interface, the emulsion composition, Presented at the September 23, 1954, Seminar, New York City.