OF THE HAIRS. 193 



their bnlbs presented processes without hairs like those which precede 

 the shedding of the ejchishes ; such processes, in fact, being of very 

 common occurrence in the hairs of chihh'cn within the first year. I be- 

 lieve I am not wrong, if from the presence of these processes I deduce 

 the universal occurrence of a shedding of the hairs, particularly as it is 

 certain that in many children within the first 2-6 months after birth, 

 the hairs of the head fall out and are replaced by new ones. How- 

 ever, further observation is necessary to determine what period is occu- 

 pied by this first shedding of the hair, in what hairs it occurs, and 

 whether perhaps the process is subsequently repeated. 



If we compare the shedding of the hairs with their first develop- 

 ment, we find a great resemblance between the two processes. In both, 

 elongated projections, wholly formed of round soft cells, shoot like buds 

 from the stratum MaJpighii, in the one case of the skin itself, in the other 

 of the hair-sacs and hairs. In both, a separation of the inner from the outer 

 cells next takes place ; and while the latter are metamorphosed into the 

 outer root-sheath, the former become the inner root-sheath and the hair. 

 The latter arises, as is still more clear in the shedding of the hairs than in 

 their first development, like the nail, with all its parts at once, as a small 

 hair provided with point, shaft, and root, and which only subsequently 

 begins to grow, in consequence of which it enlarges in all its parts, 

 and finally reaches the surface. The difi'erences between the two modes 

 of development are very inconsiderable, and chiefly depend upon the 

 rudimentary hair-processes, in the one case proceeding from the hairs 

 themselves, but not in the other; and upon the circumstance that the 

 young hairs, although in both cases they lie at first in a closed space, 

 reach the surface more readily in the one case, than in the other. 



In the periodical shedding of the hair of animals, the observations 

 of Heusinger and Kohlrausch, and lately those of Langer, Gegenbaur, 

 and Steinlin, show that the new hairs are also developed in the sacs of 

 the old ones ; although, according to the last author, with whom how- 

 ever Langer is not quite in accord, the process does not appear to be 

 exactly the same as in man. 



§ 64. Pliysiological Observations. — The hairs have a definite length, 

 dependent upon locality and sex, but if they are cut they grow again, 

 and consequently exhibit the same conditions as the other horny textures. 

 The place from whence the growth of the hair proceeds is unquestionably 

 the bottom of the hair-sac. Here there arise around the papilla? with 

 the co-operation of a blastema formed out of its vessels or those of the 

 hair-sac, new elements, by the continual multiplication of the existing 

 cells, while those which are already present, somewhat higher up pass 

 uninterruptedly, the middle ones into medullary cells, the next into cor- 



13 



