SECT. 66.] HAIRS. 121 



The fully-developed hair, although destitute of vessels, is not a 

 dead structure. Although the vital changes going on in it are 

 still altogether shrouded in obscurity, still we may assume, that it 

 is permeated by fluids, and employs them for its nourishment and 

 maintenance. These fluids come from the vessels of the papilla 

 and follicle, ascend probably in chief part from the bulb, through the 

 cortical substance, and penetrate into all parts of the hair, although 

 there are no special canals for this purpose to be found in the 

 tissue. When these fluids have served for the nutrition of the 

 hair, they are exhaled from its outer surface and replaced by new 

 portions. Perhaps, also, the hairs absorb fluids at the surface, 

 cither as liquid or vapour, exactly like a hygrometric hair; on the 

 other hand, I cannot believe that the secretion of the sebaceous 

 glands penetrates the hairs from without, as many authors appear 

 to assume, since the perfectly-continuous hair-cuticle is, in fact, 

 impervious to it. In like manner, it appears to me still by no 

 means proved, that the hairs are permeated by a special oily fluid 

 (Laer), coming from the medullary substance (Heichert), and 

 keeping them in an unctuous condition; for such a fluid cannot 

 be demonstrated, and the unctuous character of the hairs is easier 

 explained by the sebaceous secretion of the skin, which, as may be 

 easily seen, adheres to them externally. The formation of air in 

 the medulla can depend only upon a disproportion between the 

 supply of fluid from the hair follicle aud that which goes off by 

 evaporation ; it is, as it were, a desiccation of the hairs, although 

 it must not be thought that the hair is entirely deprived of 

 moisture in its aeriferous portions. But, doubtless, the aeriferous 

 portions are to be regarded as the most inactive, and as relatively 

 dead parts of the hair, whilst the fibrous substance, which is also 

 easiest altered by the action of alkalies, notwithstanding the 

 apparent hardness and rigidity of its elements, must be considered 

 as richest in fluids, and as taking the largest share in the nutrition 

 of the hair. The hair must, therefore, be regarded as endowed 

 with life, and dependent in a certain way upon the entire organism ; 

 but upon the skin, in particular, from whose vessels (those of the 

 hair-follicle) it draws the materials necessary to its existence. 

 From the condition of the hairs, therefore, as Henle aptly observes, 

 we may draw a conclusion of the degree of activity of the skin 

 it -elf. If they be soft and shining, the skin is turgescent and 

 actively exhalent ; if they be dry, brittle, and rough, we may infer 

 a certain degree of collapse of the surface of the body. The 

 failing out of the hairs certainly depends, in many cases — -as, for 



