196 SPECIAL HISTOLOGY. 



ing to Heusinger's observations, the whiskers of dogs, when pulled out, 

 are produced from the same sacs in a few days, and also that during the 

 shedding of the hair in adult animals, according to Kohlrausch, the 

 young hairs are produced from the old sacs. Also, when the hairs 

 which have fallen out after a severe illness, are replaced, it is more 

 probable, since, according to E. H. Weber, the sacs of lost hairs remain 

 for a long time, that they arise in the old sacs, than that new ones are 

 developed.* 



The multiplication of the cells of the bulb of the hair during its 

 growth takes place unquestionably, not by free cell-development, since 

 no trace of anything of the kind is to be seen in any bulb, but either 

 by endogenous cell-development round portions of contents, or by divi- 

 sion. I do not think that all those hairs which possess a sharply-defined 

 clav'ate bulb are on that account dead and ready to fall out. It is cer- 

 tainly thus in many cases ; but in others this condition indicates nothing 

 more than the normal termination of growth, whence of course, it does 

 not follow that the nutrition also has ceased. In proof of the occurrence 

 of a continual development of the hairs independently of the old hair- 

 sacs, the hairs which lie spirally curled up under the epidermis and 

 subsequently break through it, upon the forearm, leg, &c., are frequently 

 cited. But I do not know that it would not be more correct to consider 

 this, with many pathologists, rather as an abnormal process. In the 

 first place this formation of the hairs by no means occurs in all per- 

 sons ; and secondly, where it does, there are found together with those 

 coiled-up hairs, which are apparently normally developed, others which 

 are evidently abnormal, in great quantities. These, often in consider- 

 able number (up to 9), with thick sheaths, lie in one sac and have 

 rounded points, with irregular bulbs. With respect to their relations, 

 it might for the present be wiser, so long as an actual, normal new 

 development of hairs has not been demonstrated, not to assume it, and 

 to consider that, even at a later period, the development of new hairs 

 within the old sacs is the normal mode, especially since Dr. Langer has 

 actually observed it to take place in many instances in the very same 

 manner as that which I have described in children. The reason why 

 the hairs grow continually, if they are cut, but not otherwise, is the 

 same as I have already adduced, to account for the same occurrence in the 



* [Berthold (Milll " Archiv, " 1850) has communicated some curious statistics relative to 

 the growth of Hairs. The hairs of the head of a female of from 16 to 24 years of age, grow 

 at the rate of 7 lines a month. The growth of the hairs of the beard is quicker the oftener 

 they are cut; shaved every 12 hours they would attain a length of from 5^-12 inches per 

 annum ; every 24 hours, from 5-7^ inches; every 36 hours, from 4-6^ inches. They grow 

 faster by ^ during the day than during the night; and in 18 days of summer, 0026 more 

 than in 18 days of winter. TRS.] 



