246 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the death of only half of the test animals. Needless to say, MLD 50 is always smaller than MLD 100. External Toxicity. This includes irritation of the skin, scalp, eye and mucous membranes. Three methods are currently used, all of them satisfactory within their own scope: (a) The animal intradermal injection method. This is the quickest, most accurate and inexpensive screening method. It is used with advan- tage before starting more elaborate and expensive investigations. For this reason, and because of the fact that it obtained wide acceptance during the past few years, it deserves a complete description. The main feature of the method is the preparation and injection of sterile extracts. The extracts of cosmetics or their compounds are made in an autoclave at a pressure of 15 pounds for twenty minutes. As the best extracts are isotonic, the vehicle of choice is normal physiological saline solution, containing 0.85 per cent of sodium chloride in freshly distilled water. However, when it is known that the substance to be tested is in- soluble in normal physiological saline solution, it can be extracted in sterile U.S.P. olive oil. Experience based on several thousands of tests in- dicates that the concentration of the extract should be 5 per cent whenever such materials would normally be patch-tested in their natural state on human subjects. The amount of the sterile extract to be aseptically injected is usually 0.5 cc. It seldom varies. Only the concentration of the extract is sub- ject to changes. The injection is absolutely painless and the elimination of the injected solution starts immediately after the injection. The results are obtained twenty-four hours after the injection. They show reactions which can be divided into five categories, or the absence of irritation. As stated before, the main purpose of the animal intradermal single in- jection method is to obtain rapid screening results in the determination of the presence of primary irritants. However, if an injection of the same amount of the same cosmetic is made on the same animal ten to fifteen days after the first one, it will indicate whether the cosmetic is a cutaneous sensitizer or not. The method is especially useful when the first injection indicates the absence of primary irritants prior to conducting a patch test on human subjects. Such a patch test is definitely unnecessary when either of the two injections shows positive results. Advantages of the method: 1. It is simple: no method is easier to apply. Any biology technician can use it. For this reason it has replaced the obsolete method of animal patch tests. 2. It is accurate, so much so that its results are almost always confirmed by the prophetic patch test.

NEW TRENDS IN COSMETIC EVALUATION 247 3. It is reproducible on any number of animals when the same extract is injected. 4. It is rapid, can be made in thirty seconds per extract, and the results are always available twenty-four hours later. 5. Finally, it is the most inexpensive of all toxicological methods of proved value. (b) The Draize eye irritation test. It is used on cosmetics which come normally or can come accidentally in contact with the tissues of the eye. It consists of instilling an aliquot of the cosmetic or an extract of it in the conjunctival sac of animals and evaluating the degree of irritation caused on the various tissues of the eye after various periods of time following the installation. (c) The United States Public Health Service Prophetic Patch Test. This is considered as the most reliable method for the detection of primary irritants and cutaneous, despite its imperfections. As we understand that patch test methods will be described in this issue by Klauder we will omit this part of the toxicological investigations of cosmetics in deference to the author. P^c•:^G•rG of Cos•rETmS Since we published the first edition of our book: PACKAGING EN- GINEERING in 1954, which contains a special chapter on the packaging of cosmetics, a few new packaging materials and methods have appeared on the American market. Consequently, it appears necessary to review these additions, as some of them are of interest. Bacteriology The most valuable improvements in the bacteriology of packaging materials consist in the treatment of soap wrappers and cardboard boxes, with mildew and germ-repellent chemicals of low toxicity. It can be said that most products used today for this purpose are satisfactory and there is no excuse anymore for mildewed soap wrappers or contaminated face powder containers. Odor Transmission This used to be the greatest packaging problem in the cosmetic industry. Some materials still in use leave a great deal to be desired in this respect, but many others are quite acceptable. Unless especially manufactured for this purpose, no packaging materials except metals are odor transmission- proof. Paper, cellophane, cardboard, plastics, glass used in containers, covers, stoppers all allow odor transmission fi'om within or without or both. Intrinsic odor transmission can be verified by measuring the in- tensity of the odor of a cosmetic as it leaves the factory and after various periods of time of shelf life under various conditions of temperature, hu-