170 SPECIAL HISTOLOGY. 



projecting far forwards, which is presented in all nails, is worthy of 

 remark. It is considerably thinner and narrower than the body, and is 

 separated from it by a semilunar line; it is rounded anteriorly, as much 

 as 2 lines long, and is plainly nothing but the nail of an earlier period 

 which has been thrust forward by the longitudinal growth of the nail in 

 the course of its development. In fact it nearly corresponds in size with 

 a nail of the sixth month. 



Soon after birth the long free edge of the nail of the new-born infant 

 is cast off, at least once (according to Weber many times), in all pro- 

 bability in consequence of external mechanical violence, which it is 

 unable, owing to its delicacy, to resist. In the sixth and seventh months 

 after birth, I find that the nails which the child brought into the world, 

 are completely replaced by new ones, and in the second and third years 

 the nail-plates are not distinguishable from those of the adult, whence 

 it follows that the nail increases in thickness, less in consequence of any 

 enlargement of its elements, than by the addition of new ones to its 

 edges and under-surface. 



The investigation of the nail-cells and plates is best made in fine 

 sections of recent nails, with and without the addition of reagents, 

 especially caustic soda and sulphuric acid, concerning whose operation 

 the most important points have already been noted. To examine 

 the relations of the parts of the nail to one another, and to the epi- 

 dermis, the nails must be separated from the cutis by maceration, or by 

 boiling in water. It is then seen, that the nail is detached, with the 

 cuticle, from the finger ; and in transverse and longitudinal sections, its 

 mode of connection with the former is perceived. The bed of the nail 

 also, its lamince and ridges, the fold and the lamince in the stratum 

 Malpigliii of the nail, are easily seen, in this way. Since fine sections, 

 in such a nail, are not readily made, precisely in the most important 

 parts the margins and roots, it is necessary, for this purpose, to 

 employ fresh nails separated from the bone with the cutis, and dried. 

 These afford all the information required, portions of them swelling up 

 readily in water, and exhibiting the structure of the different layers, 

 with acetic acid and caustic soda, in the most distinct manner. 



Literature. A. Lauth, " Sur la disposition des ongles et des poils," 

 Mem. de la Socidte' d'hist. nat. de Strasbourg, 1830-4 ; Gurlt, " Ueber 

 die hornigen Gebilde des Menschen u. der Haussaugethiere," Mull. 

 "Arch.," 1836, p. 262; Reichert, in Mull. "Arch.," 1841, Jahresbe- 

 richt; 0. Kohlrausch, "Recension von Henle's allgem. Anat.," in Get- 

 ting. " Anzeigen," 1843, p. 24; Rainey, "On the structure and forma- 

 tion of the nails of the fingers and toes," in "Trans, of Microsc. Society," 

 March, 1849; Berthold, "Beobachtungen liber das quantitative Verhalt- 

 niss der Nagel- u. Haarbildung beim Menschen," in Mull. "Arch.," 1850. 



