II.—Observations on the Relative Rate of Growth of the Nails of the Right and Left Hands respectively: on Seasonal Variations in the Rate, and on the Influence of Nerve-section upon it

Summary

The growth of the finger nails has been investigated, and the rate on the right side as compared with the left, and in summer as compared with winter, determined for each finger. In nearly every case the rate is faster in summer than in winter.

In nearly every case also the rate is faster on the right hand than on the left. A notable exception is presented by the thumb nails, which have grown faster on the left hand than on the right both in summer and winter. The slowest rate of growth occurred in the nail of the little finger of the left side. The cutaneous nerves (ulnar) of this finger had been severed, and, with the exception of those which subserve pain, had not shown functional recovery. It is therefore probable that a trophic influence is exercised through the nerves upon the growth of the nail; the probability being supported by the fact that the little-finger nail on the left or de-nervated side not only exhibits a slower rate of growth but is distinguished from the corresponding nail on the normal side by being more flattened in form, rougher on the surface, and more brittle in texture.