THE SKIN. 295 



The tissue of the nail is nourished by blood from the bed of 

 the nail and from the nail-fold. Nails grow more rapidly in 

 children than in adults, and more rapidly in summer than in 

 winter. The rapidity of growth varies according to the person 

 and the particular nail. The rate of growth in individual nails 

 can be learned by observing the rate of progress toward the free 

 margin of the white spots seen on nails. 



The nail begins to form in the third month of intra-uterine 

 life as a fold covered with a layer of embryonic epidermic cells. 

 In the fourth month a layer of new cells, which afterward be- 

 come the horny cells of the nail, appear between the rete Mal- 

 pighii and the embryonic epidermic corpuscles. At the fifth 

 month the epidermic covering disappears and the nail lies ex- 

 posed. Between the sixth and eighth months the nails are 

 somewhat firm, but do not quite extend to the ends of the 

 fingers. At the eighth month the nails are well developed and 

 extend to the extremities of the fingers. 



For the .microscopical study of the horny part of the nail, 

 sulphuric acid, or caustic soda, or potash must be employed to 

 soften the corpuscles. For the other structures of the nail no 

 special procedure is necessary. 



BIBLIOGRAPHY. 



WAGNER. Miiller's Archiv. 1852. 



MEISSNER. Beitrage z. Anat. u. Phys. d. Haut. Leipzig, 1853. 



OEHL, E. Annali univ. di med. 1857. 



KRAUSE. Die term. Korp. d. einf. Sens. Nerven. Hannover, 1860. 



SCHROEN. Contrib. alia anat. fisiolog. e patholog. della cute umana. Torino, 1865. 



AUPPHAMEU. Wurzburger Verhandlungen. Band I. 1809. 



TUOMSA. Arch. f. Derrnat. 1873. 



LOTT. Ueber den feineren bau u. die phys. Regeneration des Epithels. Leipzig, 



1874. 



THIN. Journal of Anat. and Phys. Vol. VIII. 1874. 

 HEYNOLD. Ueber die Knaueldriisen des Menschen. Virchow's Archiv. Bd. LXI. 



1874. 



UNNA, P. Archiv f. mikrosk. Anat. XII. 1876. 

 FISCHER, E. Ibid. 



RAVOGLI. Med. Jahr. Wien. H. I. 1879. 

 RANVIER. La France medicale. January, 1880. 



