SECT. 66.] HAIRS. 1 23 



reproduced, it is more probable that they are developed in the old 

 follicles than that they are entirely new formations ; since, accord- 

 ing- to E. II Weber, the follicles of cast-off hairs continue to exist 

 for a long time. 



The reason why the hairs continue to grow, as long as they are cut, othei*- 

 wise not, is the same as I already adduced in the analogous case of nails. 

 The vessels of the papilla) yield a certain quantity of nutritive fluid, just so 

 much as suffices to keep the whole hair continually moist, and to maintain it in 

 a state of vitality. If the hair be cut, there is more nutritive fluid present 

 than the hair requires, and thus it grows from the surplus of the supply, 

 until it has again attained its typical length, and so it continually grows, if it 

 be continually clipped. 



Dzondi, Ticfenbach, and Wiedemann, have succeeded in transplanting the 

 hairs with their follicles. Hairs arise, also, in abnormal localities, e.g. on 

 mucous membranes, ovarian cysts, encysted tumours, and possess in all these 

 cases, even in the lungs (Mohr's case), follicles, root-sheaths, and an otherwise 

 normal structure. Cicatrices of the skin remain destitute of hairs. We 

 cannot say upon what depends the occasional occurrence of excessive growth 

 of the hair, or of an abnormal general shedding, together with repeated repro- 

 duction. Probably increased or diminished exudation from the vessels of 

 papilla? and hair-follicles are the chief, the condition of the skin, and of the 

 entire organism, the remote causes of these phenomena. Baldness, limited 

 to a particular spot {alopecia circumscripta), may be caused by vegetable 

 growth (fungi) in the interior of the hair itself, or under the cuticle of the 

 hair, and around it. The turning gray of the hair is also unexplained, 

 although the nervous system may evidently be concerned in causing it (grief, 

 arduous mental exertions). It is not until physiology and chemistry have 

 made us better acquainted with these last-mentioned processes, that we can 

 think of a scientific pathology and therapeia of the hair. 



For microscopical examination, a white hair with its follicle should be 

 selected, afterwards also coloured ones. Transverse sections may be procured 

 either by shaving twice at short intervals (Henle), or cutting hair upon a 

 glass (II. Meyer), or a bundle of hairs between two cards (Bowman), or 

 grasped in a cork (Ilarting) ; lieichert uses for this purpose hairs fixed in 

 gutta percha. Longitudinal sections may be obtained by scraping a fine or 

 splitting a coarse hair. The hair-follicle may be examined, isolated, and with 

 the hair ; its different layers may be separated by a nice dissection, and the 

 nuclei of the two external ones may be perceived on the addition of acetic 

 acid. As to the papilla we have already given the necessary information. 

 The outer root-sheath, with its upper part, often wholly accompanies the hair 

 when torn out ; in the macerated skin it is very easily detached with the 

 hair ; the cells may be seen without addition, or by means of a little acetic 

 acid or caustic soda. The inner root-sheath is often found entire in torn-out 

 hairs, and may, without further preparation, or after removal of the outer 

 sheath, be seen in all its parts. Potash and soda make it still more distinct 

 after they have acted for a short time. The hair-cuticle must be examined 

 particularly with alkalias and sulphuric acid, as also the hair itself ; what is 

 most important in reference to this has been already mentioned, and for 

 further details consult Bonders (1. c). I will only mention that here also the 



