SECT. 53 ] NAILS. IOI 



rightly regarded as a modified part of the epidermic horny layer, 

 of the terminal segments of the fingers and toes. 



§ 53- Growth of the Nails. — So long as they are cut, the nails 

 continue to grow; but if not pared, their growth is limited. In 

 this case, as is observed in bed- ridden patients and among the 

 people of Eastern Asia, the nails attain a length of i| to 2 inches 

 (among the Chinese, according to Hamilton, 2 inches), and bend 

 round the points of the fingers and toes. 



Dining the growth of the nail, its mucous layer docs not alter 

 its position, but its horny layer is continually pushed forwards. 

 The formation of its elements, by the conversion of the cells of 

 the mucous layer of the nail into a horny substance, takes place 

 in all parts where it is in connection with the latter; in other 

 words, upon its whole lower surface, except the free anterior border ; 

 further, in many cases, also, on a very small part of the upper 

 surface of the root; lastly, on the posterior echje of the root. 

 The parts at the root grow quickest, whilst the apposition of 

 cells to the body of the nail is slower, which is especially proved 

 by the circumstance, that the nail is not much thinner at the limit 

 between the root and the body than anteriorly on the body itself; 

 and that, at the root, the transition of the cells of the mucous layer 

 into the cells of the nail is easy, on the body, on the other hand, 

 difficult of demonstration. By the continual addition of new cells 

 at the margin as well as on the lower surface of the root, the nail 

 grows forwards, and, by the addition of such cells to the lower surface 

 of the body, it becomes thicker. The growth in the longitudinal di- 

 rection surpasses that in thickness, firstly, because the first round 

 cells, as they advance from behind and below, forwards and up- 

 wards, become more flattened and elongated; and, secondly, 

 because the formation of cells is much more energetic at the root 

 than anteriorly. The plates of the nail, when once formed, become 

 continually flatter and harder as they move forwards and upwards ; 

 however, they never lose their nuclei. Beyond these changes, the 

 elements of the hornv layer of the nail are not further altered, 

 and present the same anatomical and physiological characters, in 

 general, as those of the perfectly formed hair and of the horny 

 layer of the epidermis. 



With reference to the pathological conditions of the nail, I may observe 



that the nails are easily regenerated when they fall off, in consequence of 



bruises, burning, freezing, cutaneous diseases {e.g. scarlet fever), inflammations, 



. lations, suppurations, and effusions of blood in the bed of the nail ; i t 



