Figure 6. Cryostat sections of skin biopsies. The stratum corneum has been demonstrated by the Mackenzie technique. (a) is from the control site (b) is from the site treated by salicylic acid.

Evahtation of emollients and keratolytics 435 the test site is photographed so as to give a final magnification of five to eight times. We decided to employ this technique in the evaluation of one emollient. In order to quantify any changes we arranged to measure the width of the skin furrows at five sites chosen in a standardised way by placing the photographs under a template. To remove all bias the photographs were coded and the observer who performed the measurement had no knowledge from which subject or treatment group the photographs came. For the actual measurement a x 8 magnifying lens with built in measuring graticule was used. This experiment was performed on six individuals with normal skin and six with dry skin and was over a 4 h period after application of an emollient (Table II). Table 1I. Skin furrow width determined from photographs in six normal and six 'dry skin' subjects Time (min) Furrow width (mm + S.D.) Dry skin subjects Normal subjects Control 1.41 + 0.20 1.34+ 0.19 0•' 1.51 +0.16 1.54+0.16 30 1.80 + 0.37* 1.54+ 0.21 60 1.57+0.11 1.54+0.12 120 1.52+0.16 1.37+0.15 240 1.77+ 0.40 1-43 + 0.26 * Difference from control (P =0.05) •' Immediately after application I do not know why furrow width decreases after hydration but there seems to be little doubt that it does and this can serve to give a quantitative index of hydration effect. Scanning electron microscopy (SEM) has been used by several groups including ourselves to assess the effect of hydrating agents (3, 4). In our experience SEM of skin surface replicas or skin surface biopsies (4) can certainly detect alterations after application of HA but they are difficult to quantify. The most prominent change in replicas is the 'filling up' of the normal surface furrows (Fig. 1). In addition, individual cell margins are more prominent and the cells appear plumper (Fig. 2). Because this is a very cumbersome (and costly) technique and gives no quantitative data, it is, however, best to choose another way of testing HAs. (C) SURFACE CONTOUR ANALYSIS Replicas of the skin surface show quite marked changes after application of HA. The replicas that we now employ reproduce the surface contour with an astonishing resolu- tion (Fig. 3). We use 'Silflo' dental impression material (a silicone rubber material) for the negative and we then coat the negative with 'DPX' (a styrene plastic slide mounting medium). The 'positive' is dried in a desiccator overnight and then separated from the 'negative'. After separation the positive is mounted on a glass microscope slide and subsequently its surface contour is traced using an instrument known as a surfometer (6). The stylus of this instrument barely indents the surface and the excursions of the stylus give an accurate representation of the surface contour of the specimen. All the HAs tested in this system show a decreased contour profile in the few hours following their use. The decrease in contour profile is consistent and time dependent but not dramatic. In one series of tests six normal volunteers and six volunteers with 'dry' but otherwise normal skin used a popular (oil in water emulsion lotion) on the lower legs and replicas