THE SKIN. 195 



safe because they had no perceptible wound, and therefore 

 exposed themselves to very virulent poison, have been infect- 

 ed by the poison's insinuating itself through the very slight 

 rupture of the cuticle on the end of a finger, where a mere 

 hangnail had been raised. 



458. Other parts, that grow out of this cuticle, have the 

 same structure, and are endowed with the same properties. 

 The nails of our fingers are productions from this membrane, 

 condensed and made firm. Yet they have the same power to 

 protect, and the same insensibility. The hoofs of horses, the 

 horns of cattle, are similar; they have the same protective and 

 the same negative character. 



459. The nail grows from the cuticle. It has its root 

 (Fig. XXVII. c) in the inner layers of this membrane, and 

 its under surface is closely attached to the true skin. It 

 grows from the root forward. 



FIG. XXVII. Vertical Section of the Thumb and Nail. 



a, Nail. 

 &, Cuticle. 



c, Root of the nail. 



d, True skin. 



/, Fatty matter under the skin. 

 g, Bone. 



460. The hair (Fig. XXVIII. 6, c, &,) is composed of a sub- 

 stance similar to that of the cuticle. It takes its origin in a 

 pulpy bulb, (Fig. XXVIII. d,) which is situated below the 

 true skin, (Fig. XXVIII. /.) It is fed by an artery, (Fig. 

 XXVIII. ,) which supplies it with the material of growth. 

 Within the skin, it is a tube containing a pulpy matter, (Fig. 

 XXVIII. c.) In ill health, or in the later periods of life, this 

 nutriment diminishes and the coloring matter ceases, and 

 then the hair is white. Still later, the nutriment entirely 

 fails, and then the hair falls out, and the aperture in the skin 

 closes. 



461. The cuticle is continually casting off its outward layer 

 in the form of little scales, so minute as to seem like dust ; 



