OF THE HAIRS. L93 



also it happens, that the cells even of a complete hair-bulb are 

 to be regarded as the successors of those of the foetal hair.] 1 



§ 63. 



Shedding of the Hair. —After birth, a total shedding of the 

 hairs takes place in consequence of the development of new hairs 

 within the hair-sacs of the lanugo, which gradually force oat the 



old ones. This shedding of the hairs, which I discovered in 

 the eyelashes of a child of one year old, commences by an 

 outgrowth of the soft round cells of the bulb and of the neigh- 

 bouring outer root-sheath, from the bottoms of the sacs of the 



1 [From what has been said above (see note on the Cuticle) it is clear we do not 

 share Professor Kblliker's view that the hair is an epidermic production. Reichert's 

 view, on the other band, that the hair results from the cornification of a dermic 

 papilla or matrix, which drying up and becoming filled with air, remains as the me- 

 dullary portion, seems to us to be nearer the truth. There can be no doubt of these 

 two facts : I, that no line of demarcation can be traced between the papilla of the 

 hair and its shaft ; and 2, that in many animals the papilla is vascular and nervous for 

 a considerable distance into the shaft, and, therefore, is certainly a dermic structure. 



Whether Reichert's somewhat mechanical notion of the " drying up" of the matrix 

 to form the medulla is correct, is not of much importance, so long as wc keep in 

 view the unquestionable continuity of tissue anil bomological identity, of the medulla 

 and cortex with the dermic papilla. 



For us, in fact, the Hair is homologous in all its parts with the Tooth. The sub- 

 stance of the shaft corresponds with the dentine, offering even rudimentary tubes 

 in its aeriferous cavities; the inner layer of the cuticle answers to the enamel, the 

 outer to Nasmyth's membrane ; and whoever will compare these structures will be 

 struck by the similarity even in their appearance. The sac answers to the dental 

 capsule; the outer root-sheath to the layer of epithelium (enamel organ) next the 

 capsule; the fenestrated membrane to the stellate tissue; and what Professor 

 Kbllikcr calls " Huxley's layer," to the columnar epithelial layer of the organon 

 adamant in (p. The comparison may seem startling at first, but the examination of 

 the development of the teeth of an osseous fish, for example, will suffice, we believe 

 to afford full justification of it. 



With respect to the not very important question, as to the nature of the first rudi- 

 ment of the hair-shaft, i. e. whether it is the point of a hair or a whole bair, we must 

 confess that we should be tempted to arrive at the opposite conclusion to our author, 

 inasmuch as the portion of the hair which first appears becomes the point of the 

 fully-grown hair, we should say that the hairs are formed like the teeth, point first. 



A hair, like a tooth, has a definite form to attain. As the latter has a peculiarly 

 constructed and narrowed root when complete, so has the bair when it has attained 

 its full growth a peculiarly constructed bulb; and it is not a perfect hair until this 

 peculiar bulb is developed. Until it has attained this form it goes on growing; but 

 once having reached it, it grows do more, but falls out and is replaced by a new 

 bair (see following §). — Eds.] 



i. 13 



