MODERN TRENDS IN COSMETIC FORMULATION stratum corneum of the skin has classified these as keratin, lipids, water- soluble hygroscopic surface-active agents and a "cementing" substance which binds the cornified cells together and to the underlying layer. The water-soluble agent can be extracted from the intact skin if the latter is first washed with a detergent or a solvent and then washed repeatedly with water. After extraction, it is found to consist substantially of a mixture of sixteen free amino acids and to contain smaller amounts of urea, lactates, various metallic salts and a number of other compounds. Observations have been made which link this composition with behaviour. Horny tissue from which the hygroscopic material has been extracted becomes water-repellent but at the same time the stratum corneum, once deprived of this substance releases water vapour from the underlying tissues almost three times faster than normal stratum corneum. A deficiency of the extractable material occurs in senescence and in some pathological skin conditions. In studies of the horny layer of the skin a low water-binding ability was found to be associated with a low alpha-amino nitrogen content and normal hygroscopicity was associated with high content. • This accords with the fact that the water-soluble hygroscopic material derived from the skin is rich in free amino acids. The hypothesis that this material aids in moisture retention by the skin, is reasonably well established, but the added hypothesis that, once extracted, it can be applied externMly to restore impaired ability to retain moisture is not convincingly proved. The evidence put forward is based upon observations which do not appear to have been safeguarded by an adequacy of controls. Quantitative results cannot be achieved by methods of observa- tion which are of doubtful qualitative value. A hygroscopic material rich in amino acids has been reported in hair as well as in skin •9 and the interesting suggestion has been made that the amino acids and polypeptides in this mixture help to keep the hair in good condition. 2ø It was shown that complete stripping of the free amino acids from the hair during shampooing can be avoided by adding amino acids to the shampoo in a suitable concentration. By a radiochemical technique, observations were made on a quantitative basis to show that a balance can be achieved between the amino acids stripped from the hair and sorbed by the hair from the shampoo. TISSUE EXTRACTS. BIOGENIC STIMULANTS. The work of Filatov et al. in Russia 2• aroused interest in France and Germany, in the properties of biological fluids and gave rise to the so-called tissue and serum therapy in the realm of cosmetics. Filatov placed living plants under marginal survival conditions, at a temperature of 2ø-4 ø C in darkness, for several days and then extracted the leaves with ether. The

202 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS soluble substances in the ether were found to exert a stimulating effect upon the growth and respiration of yeast cells, and upon the growth of seedlings. It was reported that application of the extracted material to wounds in the rabbit speeded up the rate of healing. Opinion at the present time is that it is a practical impossibility to note with any certainty any effect at all of any external application upon the rate of healing of a wound. There is a time lag before any distinct cell proliferation can be observed and when that is over, a matter of a day or two, the rate of healing is so rapid that comparisons cannot be made. The preliminary period during which nothing appears to happen cannot at the present time be reduced or eliminated. It is of course practicable to observe a c. leansing action taking place. Filatov put forward the view that when an organism is submitted to conditions in which it is difficult to survive, substances are formed which fortify the organism and help it in the struggle for survival. These are amongst the substances extracted by ether in his experiments and are responsible for the stimulating action of the extracted material upon living cells. A chemical examination of the extracted material followed and it was found that cinnamic acid, hydroxycinnamic acid and some of their derivatives were present. These were regarded by Filatov of some importance because of their property of acting as hydrogen acceptors. Thus they might be expected to influence the oxidation-reduction mechanism of any organism into which they were introduced. Filatov proceeded to show that dilute solutions of cinnamic acid, its sodium salt, coumarin and the sodium salt of coumaric acid all produced stimulating effects similar to those produced by the extracts prepared from the leaves of aloes after survival of the plant under marginal conditions of existence. From this starting point, the French and German workers proceeded to extend the range of tissues submitted to extraction, and particular stress was laid on animal tissues closely concerned with active cell proliferation as for example the placenta of mammais and various parts of the developing embryo. Particular importance was p!aced upon modification of the extrac- tion process, in order to preserve as completely as possible the whole of the extractable cell contents. Filatov's procedure led to the inactivation of such unstable substances as the enzymes. Very definite effects upon the rejuvenation and general toning of the human skin have been described after external application of cosmetic preparations containing these extracts, despite the extraordinary difficulty of comparing the effects upon the intact human skin of any two externally applied cosmetic preparations. Numerous tests have been applied to tissue extracts with the expressed intention of evaluating their activity, and they include