FET.\L EPIDERhlIS 131 ':"'"'i.•"":"'" ' ,: .... :i]• & '• ............ ½.•½ '• ',,½: ':'."•-,.'• ' •,. ½•Y.,• :,•.•-.-,....•.-•,•,,,.•..,.,•75. •: •:S& ,.•...•2 • Figure 7. Demonstration of sulfhydryl groups in epidermis of guinea pig fetus by DDD methyl of Barrnett and Seligman (6) A. Guinea pig skin 40 days after concep- B. Guinea pig skin 60 days after concep- tion. Lack of contrast in micrograph tion. Strong --SH reaction in the epidermis demonstrates the very weak reaction of --SH and especially in the hair shaft is easily ob- (x 312) scrvcd (X 312)

132 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS In general, histochemical observations showed a good correlation with the analytical data during the prenatal period. The --SH reaction showed up in later stages as a diffuse monocoupling reaction throughout the epidermis. The high --SH level seen in the hair shafts at the 61st day (Fig. 7) would not have been measured in the chemical analysis for --SH since only hair-free epidermis was used. Studies in the Rat Fetus Barrier Function Because of tissue fragility, the water permeability of fetal rat skin could be determined for only a few days before parturition (Table IV). Table IV Water Permeability and Epidermal Sulfhydryl Content of Skin of the Fetal and Newborn Rat Body Crown- Weight Rump (Wet) Length (g) (cm) Estimated Water Diffusion Sulfhydryl Sulfur a Age No. of Rate a "Total .... Free" (days) Animals (mg/cm2/hr) (mg/gm dry weight) 32 34 36 36 37 38 39 41 56 6.0 6.2 6.5 6.9 7.9 11.0 13.4 13.6 21.0 26.9 34.8 2O0 3.2 3.6 3.4 3.7 3.6 3.9 3.6 3.8 4.2 4.3 4.5 4.5 4.7 4.9 5.2 56 58 58 74 Prenataff 5 0.94 Prenatal 2 0.78 Prenatal 5 0.66 Prenatal 4 0.48 Prenatal 3 0.78 Prenatal 4 0.70 Prenatal 4 0.38 Prenatal 3 0.35 Prenatal 5 0.16 At birth 5 0.11 At birth 4 0.13 1 3 0.11 1 4 0.17 4 3 0.19 5 2 7 3 0.28 9 4 0.21 12 2 14 3 0.32 16 2 Adult 5 0.17 4- 0.24 -4- 0.15 +0.10 4- 0.06 4-0 02 4-013 4-0 05 4-0 06 4-001 4-OOl -bO 02 4-OOl 4-0 02 4- 0.04 4- 0.06 4- 0.02 1.94 4- 0.42 1.67 4- 0.08 3.59 4- 0.36 2.59 4- 0.30 3.27 4- 0.88 2.66 4- 0.25 2.04 4- 0.69 1.78 4- 0.54 2.33 q- 0.41 1.94 4- 0.26 2.01 4- 0.37 1.39 4- 0.29 1.17 4- 0.18 1.16 4- 0.25 q- 0.04 1.13 4- 0.05 0.73 4- 0.06 4- 0.02 0.23 4- 0.02 ... Means and standard errors (N 2) or means and average deviations (N -- 2). Skin from fetus late in gestational period (18-20 days).