6 EVENINGS AT THE MICROSCOPE. 



is just thrice as thick as the hair that we have been 

 examining, or j-J-^th of an inch in diameter. The sinuous 

 lines across the surface are proportionally far finer and 

 closer together, and no saw-teeth are visible at the edge, 

 the most delicate adjustment showing only a minute undu- 

 lation in the outline ; that is to say, the overlapping scales 

 are far thinner, and therefore their terminations are 

 nearer together, in the hair of the Swine than in that of Man. 

 I will now show you a transverse section of a similar 

 bristle, which I will obtain thus : I take this old brush, 

 and with a razor cut off one of the bundles of bristles, 

 close to the wood ; then I take off as thin a shaving as 

 I can cut, wood, bristles, and all : I repeat the same opera- 

 tion two or three times. Now, paving picked out the 

 shavings of wood, I take up with the point of my pen- 

 knife a few of the dust-like atoms that remain, and scatter 

 them on this plate (or slide) of glass, and these I cover 

 with another plate of thin glass ; for this dust is composed 

 of thin transverse slices of the bristles, and as I scatter 



contains a number of cavities filled with air, most evident in the hair 

 from aged persons, or in dry hair. 



" The central portion, the medulla, forms, when well developed, an 

 axis- cylinder, one-fifth, or one-fourth, the diameter of the hair, with 

 sharp outlines, generally central, but often a little excentric in position. 

 It is often wanting in human hair, especially in blond hair. ... In 

 woolly hair it is always wanting ; also in the hair of the new-born 

 child. The medullary substance is often interrupted, and sometimes 

 consists of only a few dark points lying in the axis of the hair . . . 

 The medullary substance has been thought to contain the pigment : this 

 is not so, the supposed pigment-granules being very minute air-bubbles. 

 The cause of the colour of the hair is found in the diffuse pigmentation 

 of the cortical substance. The cause for the hair becoming grey or 

 white is to be found in the disappearance of the diffuse pigmentation 

 of the cortical substance, the cause of which is not yet known. The 

 medullary substance can be more easily seen in white hair than in 

 coloured." (From a valuable memoir, entitled, " Hair in its Micro- 

 scopical and Medico-legal Aspects," by Dr. E. Hofman ; transferred to 

 the " English Mechanic " for May 9, 1873, from the " New York 

 Medical Journal.") 



