178 SPECIAL HISTOLOGY. 



tolerably uniform in size, but varying according to the hairs, from 

 0-0002 — 0002" and occupying the medullary cells in great 

 quantity (fig. 68). These granules are not fat or pigment, as 

 has been hitherto universally supposed, but air-vesicles, as may 

 be readily demonstrated by boiling a white hair in ether or 

 oil of turpentine, in both of which cases the medulla becomes 

 quite clear and transparent. If such a hair, treated with 

 water, be dried between the fingers, it soon, often quite sud- 

 denly and visibly to the naked eye, assumes its previous white 

 colour, and if immediately after drying, it be placed under the 

 microscope, without fluid, or with fluid at one end only, nothing 

 is easier, than to see the re-entrance of the air and the con- 

 sequent darkening of the medulla. Not only in white hairs, 

 but in dark ones also, the medulla contains air in the fresh 

 state, only in this case it does not appear of a pure silvery 

 white, but with a blonde, red or brown tinge ; this does not 

 arise from any special pigment, which is only found occasionally 

 in the medulla of dark hairs, but proceeds from its being 

 seen through the coloured cortical substance. A more careful 

 investigation of the medullary cells shows, that while fresh they 

 contain many small cavities in a viscid substance ; in these lie 

 the air vesicles, which communicate to them the granular 

 appearance above described. If we observe the air which has 

 been expelled refilling the medulla of a dried hair, it seems as if 

 all the cavities of one and the same cell communicated with 

 one another, at least the air frequently passes in continuous 

 winding streams from one cavity into the other; indeed from 

 the sudden manner in which the air sometimes fills the medulla, 

 it might almost be believed that the cavities of contiguous 

 cells were connected together. However this may be in 

 certain cases, it is conceivable, that even if the cavities of 

 the different cells are quite closed, and only separated from one 

 another by delicate partitions, the air still may quickly fill the 

 medulla under the appearances we have noted. For the rest, 

 the vacuities of the medullary cells, whether they are quite closed 

 or not, are of different sizes, the aeriferous medulla appearing 

 sometimes coarsely, sometimes finely granular. I have also 

 seen cases in which the medullary cells obviously contained 

 only a single, large air-vesicle, and appeared almost like small 

 fat-cells. Very frequently single larger or smaller spots may be 



