178 SPECIAL HISTOLOGY. 



mitted light (Fig. 65 a). If a hair thus treated be carefully teased 

 out, it is easy to isolate the medullary cells, either in aggregate masses, 

 Fig. 69. or even completely separate (Fig. 69). They are rectangular 

 or quadrangular, rarely rounded or fusiform of 0-007 0-01 

 of a line in diameter, occasionally containing dark, fat-like 

 granules, and often when the alkali has not acted too strongly, 

 a rounded clear spot of 0-0016-0-002 of a line, which is plainly 

 the rudiment of a nucleus, and which also seems to swell up somewhat 

 in soda. 



In fresh hairs, the medulla in the shaft is silvery white or dark, an 

 appearance which, as many more favorable objects show, arises from 

 rounded- angular, granular corpuscles, black (opaque) or of a brilliant 

 white, according to the illumination, tolerably uniform in size, but varying 

 according to the hairs, from 0'0002-0'002 of a line 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 ^vith water, be dried between 

 the fingers, it soon, often quite suddenly and visibly to the naked eye, 

 assumes its previous white color, 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 conse- 

 quent 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 colored cortical substance. A more careful investi- 

 gation 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 



FIG. 69. Eight medullary cells, with pale nuclei, and fatty granules, from a hair treated 

 with soda ; magnified 350 diameters. 



