TRANSCUTANEOUS ABSORPTION OF VITAMIN A 177 Oil, varied from 112 to 210 with an average of 168 units of vitamin A per 100 gm. Although the intake of vitamin A was adequate to support rates of growth of these animals and prevent the development of gross signs of a dietary deficiency of vita- min A, it did not provide an excess of the vitamin for storage in the rats' livers. Only one of the five depleted rats and one of the six negative controls gave evidence of vitamin A in their abdominal skins. In the group of four animals fed U.S.P. Reference Oil for five weeks, levels of vitamin A in skins ranged from traces to 4 mg. with an average of 3 mg. per 100 gm. The significance of these find- ings for vitamin A in skin will be discussed in a subsequent section of this report. Data for vitamin A contents of livers and for total gains in weight 'of rats in the five groups which re- ceived, during test periods of five weeks, topical applications of petro- l atum containing varying amounts of vitamin A are given in Table 2. Livers were removed for analyses from only two animals in each of the first two groups. Carcasses of the 'other rats in these groups were preserved for histological examina- tion of their viscera. Among the four groups of rats which received static, topical appli- cations of vitamin A, there is an apparent correlation between (1) concentrations of vitamin A applied to the skins and (2) total gains in weight and quantities of the vitamin stored in the animals' livers and skins within the following limits. Both maximum gains in weight and maximum, hepatic reserves of the vitamin were found for the two rats in Group I which received the greatest amounts of vitamin A applied to their skins. On the other hand, the rats in Group IV, to whose skins petrolatum containing the smallest concentration of the vitamin was applied, exhibited min- imum growth responses and mini- mum amounts of vitamin A retained in their livers. Also, this latter group showed the most variable results. Although total gains in weight were fairly uniform, i.e., from 6 to 15 with an average of 11 gm., two of the four rats gave no evidence of vitamin A in their livers, but the other two animals exhibited reserves of vitamin A equivalent to 325 and 425 units per 100 gm. of liver. No significant difference was noted between the second and the third groups in respect to either total gains in weight or stores of vitamin in the rats' livers. This statement is applicable, also, to, rates of growth for the first four weeks of the test period as summar- ized in Chart II. Comparative findings for these two groups suggest that the procedure, adopted in these experiments, is inadequate for dem- onstration of differences between the systemic effects of 135 units and 180 units of vitamin A applied to skin in equivalent amounts ofpetro- latum (0.3 gm.) daily during test periods of five weeks. Average results reported in the

178 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS table do point to a striking difference between groups III and VI in reference to both gains in weight and hepatic stores of vitamin A. The sole variation in the experimental procedure, as applied to these two groups, concerned the method of application of the petrolatum base and the vitamin to the skin. In the experiments on the third group of rats, the vitamin in the petrolatum base was spread, without rubbing, over test areas of skin (static contact) whereas, in tests on the sixth group of animals, the same smaller reserves of the vitamin for storage in their livers. A search of the biochemical, nutritional, and clinical literature reveals a paucity of quantitative data for vitamin A in human and animal skins. When due considera- tion is accorded the fact that the skin is the largest epithelial tissue of mammals, both in respect to weight and surface are% it is difficult to understand the persistent failures to include skin among the viscera analyzed in experimental studies of the distribution and storage of TASLE 2--COMPARATIVE AVERAGE LEVELS Or VITAMIN A IN LIVERS or RATS AFTER DAILY APPLICATIONS OF PETROLATUM CONTAINING VARYING CONCENTRATIONS OF VITAMIN A DURING FIVE WSEI•S No. of Units of Vitamin A Concentration of Rats per 100 Gin. Vitamin A per Gin. Analyzed Total Gains of Petrolatum in Each in Body Abdominal Groups Applied to Skins Group Wt., Gin. Livers Skins I 2100 2 62 769 20 II 600 2 36 527 16 III 450 6 34 566 13 IV 100 4 11 187 3 VI 450* 4 58 191 .. Applied to skins with massage. amount of base cbntaining equiva- lent concentrations of the vitamin was rubbed during thirty minutes of the period of contact. The comparative experimental findings, which are presented in Table 2 and Chart II, suggest that the rats in Group VI, to whose skins vitamin A was applied with mas- sage, utilized more of the vitamin for growth and, probably, also, for other metabolic processes dependent upon rapid rates of growth of young rats, than did the.rats in Group II!. Hence, rats in the former group had vitamin A. Only two publications, and both of these by one group of biochemists and nutritionists, give analytical data for vitamin A in skin. McCoord and Luce-Clausen' (7) have reported values of vitamin A in skins of rats, and Clausen and McCoord (8) have recorded results of their studies of distribution of vitamin A among tissues of human subj ects. Table 2 presents a summary of results of analyses of sections of abdominal skins of rats in groups I to IV which received static appli-