sect. 54.] NAILS. 103 



cells of the mucous layer. During its further development, the 

 nail is thickened by the addition of new cells from below, and is 

 enlarged by the extension of its elements and addition of new cells 

 at its margins; but it remains concealed under the horny layer of 

 the epidermis, even to the end of the fifth month, till at last it 

 becomes free, and, in the seventh month, even begins to grow 

 longitudinally, so that at this time, except in its greater softness 

 and different dimensions, it differs in no essential point from the 

 full-grown nail. In the new-born child, the nail is, in the body, 

 0*3' ' to o - 4 " thick, with a free border projecting 2 lines, and con- 

 sists of elongated, polygonal, nucleated plates, of o - o2'" to o - 028'". 



Soon after birth, the free border of the nail, which evidently is 

 nothing but the nail of the six- months' foetus which has been pushed 

 forwards, is thrown off at least once, or, according to Weber, several 

 times. In the sixth and seventh months after birth, the nails 

 with which the child is born, are, as I find, wholly replaced by 

 new ones; and, in the second and third year, the plates of the nails 

 differ in nothing from those of the adult, whence it results, that 

 the nail is enlarged and thickened, less from enlargement of its 

 elements, than by the addition of new ones at its borders and from 

 below. 



In the examination of the cells and plates of the nail, fine sections of fresh 

 nails are particularly serviceable, either simply or with the addition of re- 

 agents, and, above all, of soda and sulphuric acid, which cause the plates of 

 the nail to swell up. In order to make out the relations of the individual 

 parts of the nail to each other and to the epidermis, the nail and cutis must 

 be separated by maceration or boiling in water. The nail is thus detached, 

 ' along with the epidermis, from the finger, and the mode of its connection can 

 be recognised in transverse and longitudinal sections. Also the bed of the 

 nail, with its laminae and ridges, the fold of the nail and the lamina) of the 

 mucous layer of the nail, come easily into view in this way. 



As fine sections in such nails are, in the most important places, the root and 

 margin, not easily made, it is also necessary to use recent specimens, also 

 nails which have been detached with the cutis from the bone and dried, which 

 then furnish all information that could be desired, inasmuch as segments of 

 such nails easily swell up in water, and by the action of acetic acid or soda, 

 so that the structure of their various layers becomes very distinct. 



Literature. — A. Lauth, Sur la Disposition des Ongles et des Polls, Mem. de 

 la Soc. d'llist. Nat. de Strassbourg, 1830, 4. Eeichert, in Mull. Arch., 1841, 

 1851, und 1852, Jahresbericht. Rainey, On the Structure and Format/,/// of 

 the Nails of the Fingers and Toes, in Transact, oj the Microsc. Societ//, March, 

 1849. Vikchow, in Verhandlungen der Wurzburg. Gescllsch. 



