STUDIES ON THE PERMEABILITY OF THE SKIN TO MERCURY. 85 Moisture thus accumulated may produce softening and maceration of the stratum corneum, a condition which may be favorable to the re- tention of substances in close con- tact with the skin, and possibly also to penetration. While in our assays the inuncted areas of skin were al- ways kept covered to avoid con- tamination errors, it seemed desir- able to test whether this technique affected skin penetration. The re- sults are 'shown in Table 2. It is clear that covering the inuncted area increases the absorption of mercury from every one of the six different ointments tested. ß TABLE 2--EFFECT oF COVERING THE IN- UNCTED SKIN AREA ON THE CUTANEOUS PENETRATION OF MERCURY IN THE RABBIT Storage of mercury in the kidney is used as a measure of penetration Micrograms Mercury per Gram Wet Kidney Calomel Covered Uncovered Ointment Skin* Skin* 1 26 7 2 45 13 3 17 4 20 9 5 6 4 6 22 5 -- Av. 23 8 * Average of two animals on each treat- ment. 2. Location of the site of Inunction Generally speaking the abdominal skin in the rat and rabbit is con- sidered thinner than the back skin. A comparison of the penetration of mercury at these two sites was, therefore, made and is shown in Table 3. It is to be noted that the site of inunction does not signifi- cantly affect absorption of mer- cury. ' 3. Size of the'Inunction Site In spite of the best precautions, seepage of the ointments sometimes occurred so that in effect a larger area of skin came into contact with the ointment than originally planned. In Table 4 are shown the results of deliberately halving the inunction areas which were rou- tinely 8 per cent of the total body surface. The amount of mercury stored in the kidney is not halved but reduced by roughly one-third. From these data it can be inferred that small changes in exposure area cannot seriously influence the out- come of the results. 4'. Effect of IFeight, Sex, and Litter The studies were generally con- ducted on groups of rats homogene- ous with respect to age, weight, and sex, but heterogeneous with respect to litter. As examples of three pos- sible variants, litter, sex, and weight were studied. It may be presumed that these variants could operate to produce differences between skin as characterized by such factors as texture, thickness, subcutaneous fat, number of hair follicles, etc., or' differences between organs, such as the a13ility of the kidney to excrete or store.mercury. .It was found, however, that the cutaneous pene- tration of mercury, as judged by the level in the 'kidneys, is not sig- nificantly affected by the above fac- tors.

86 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE 3--EFFECT OF THE LOCATION OF THE I•UNCTION SITE ON THE CUTANEOUS PENE- TRATION OF MERCURY IN THE RABBIT Storage of mercury in the kidney is used as a measure of penetration Micrograms Mercury per Gram Wet Kidney Calomel Oifitment Back Skin Belly Skin 1 26 35 2 45 38 3 17 27 4 20 18 5 6 7 6 22 26 -- __ Av. 23 25 The results are averages of two animals on each treatment. TABLE 4---EFFECT OF SIZE OF INUNCTION AREA ON THE CUTANEOUS PENETRATION OF MERCURY IN TI-IE RAT Storage of mercury in the kidney is used as a measure of penetration Micrograms Mercury per Gram Wet Kidney Half of Calomel Standard Area Standard Area Ointment 29 (Cm.) 2 14.5 (Cm.) 2. C 5.3 3.6 D 29 23 The results are averages of six animals on each treatment. 5. Species Difference Provided the same percentage of total body area is treated with an excess of ointment, no significant difference between the skin perme- ability of the rat and rabbit can be demonstrated by measuring the 'storage of mercury in the kidney. This was tested with two 'ointments ot widely different penetrati ng [apac- ities. The results are shown in Table 5. 6. Removal of Excess Ointment Excess ointment was allowed to remain in contact with the skin routinely. The effect of removal of the excess by mechanical means causes quite a marked decrease in the absorption of mercury. This is shown in Table 6. These results are in consonance with the chemical ex- perience of Cole and coworkers (7) who have reported that there is less penetration of mercury after the so-called "clean" inunction. 7. Skin Conditioning (a) Washing. Ordinarily. the openings of the skin• such as the hair shafts and sebaceous ducts which are regarded as the avenues o'f entrance for mercury, may be partially occluded by the presence therein of cell detritus and oily secretions. Cleansing the skin with soap and water would be expected to remove some of this "plugging" material without the more vigorous effects which follow the application of lipold solvents such as alcohol or ether. However a comparative study of washed and unwashed skins in two groups of rats showed definitely that treatment of the skin with soap and water, prior to inunction, had no effect on cutane- ous penetration of mercury as measured by storage of the metal in the kidney even though the cleaning operation was seen to re- move a visible yellowish scale of dander-like material. (b) Pretreatment tfith Lard. "Softening" of the skin by thor- oughly inuncting lard into the site 24 hours before application ot a mercury ointment had a tendency