KERATIN REPLACEMENT AS AN AGING PARAMETER 541 Table 1 Age Distribution by Decade (257 Subjects) Age (yr.) Females Males 10-19 8 8 20-29 16 8 30-39 10 11 40-49 17 6 50-59 12 1 60-69 12 2 70-79 45 12 80-89 55 21 90-99 10 3 -- Total 185 72 This paper concerns itself with changes in the rate of fingernail growth with age. The work is part of a research program to develop useful pa.rameters of aging and to understand the significance of keratin replacement as a measure of physiologic function and reverse capacity. METHOD With the edge of a glass slide, a scratch was made transversely in the nail plate near the top of the lunula (Fig. 3). For this study only the thumbnails were measured. A calibrated micrometer built into a magnifying lens was used to measure the distance proximally from the scratch to the edge of the eponychium (cuticle) and distally from the scratch to the distal emergence (where the nail plate leaves the nail bed). Thus two values were obtained, distal and proximal, as a cross- check to prevent errors. Measurements were made at intervals, per- mitting the calculation of average growth in millimeters over a period of time as the transverse groove on the nail grew out. Measurements were generally taken at four- and at eight-week intervals the total growth in millimeters was then divided by the time elapsed in weeks to yield the Nail Growth Index, or NGI, in millimeter growth per week. Subjects were 257 normal males and females, selected among staff members and their families, patients with normal nails in a dermatologic practice, and residents of the Menorah Home for the Aged in Brooklyn. The ages of the 185 females and 72 males were distributed, by decade, as shown in Table I. Several studies were performed over a one-year period in order to determine seasonal changes in growth.

542 t.o o,'• JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS I•a BECBBE •57 •BdECT..R ) aGE - )'Earls Figure 5. Average Nail Growth Index per decade of 257 subjects Figure 6'. Average Nail Growth Index per decade, male rs. female RESULTS AND CONCLUSIONS The scattergram in Fig. 4 shows the average Nail Growth Index of 257 individuals in the study. Since right and left nails were found to grow at a similar rate in most individuals, the average of the two nails was used in computing the data. Broken down into decades, these figures were averaged, as plotted in Fig. 5. NGI's decreased from a