84 LECTURE II. 



Thus the nail lies in a certain measure loose, and can 

 easily move forwards, pushing itself over a moveable 

 substratum, while it is kept in place by the ridges with 

 which its bed is beset. When a section is made trans- 

 versely through a nail, we see, as already mentioned, 

 essentially the same appearance presented as that offered 

 by the skin, only that a long ridge corresponds to every 

 single papilla seen in ordinary sections of the skin ; the 

 undermost part of the nail has slight indentations cor- 

 responding to these ridges, so that, while gliding along 

 over them, it can execute lateral movements only within 

 certain limits. In this manner, the body of the nail 

 which grows from behind moves forwards over a cushion 

 of loose epidermic substance (Fig. 17, a) in grooves 

 which are provided by the ridges and furrows of the bed 

 of the nail. The uppermost part of the nail, if examined 

 when fresh, is composed of so dense a substance that it 

 is scarcely possible to distinguish individual cells in it 

 without applying reagents, and at many points an 

 appearance is presented like that which we see in car- 

 tilage. But by treating it with potash, we can convince 

 ourselves that this substance is composed of nothing but 

 epidermis-cells. From this mode of development you 

 will see how easily intelligible distinctions may be drawn 

 between the different diseases of the nails. 



There are diseases of the bed of the nail which do not 

 affect the growth of its body, but may give rise to 

 changes in its position. When there is a very abun- 

 dant development of cells in the bed of the nail, the body 

 may be pushed upwards (Fig. 17, V) ; nay, it sometimes 

 happens that the nail, instead of growing horizontally, 

 shoots perpendicularly upwards, the space underneath 

 being filled with a thick accumulation of the loose 

 cushiony substance (Polstermasse) (Fig. 17, c). Thus 

 suppuration may take place in the bed of the nail with- 



