be traced. They commence at a small distance from the bulb. In the 

 shrew, mole, and others, the development of cells is intermittent. In 

 the terminal portion of the hair of the omythorynchus they resemble a 

 rope of onions ; in other parts they are flattened discs. 



In the rat there is only one row of cells, but these are so peculiar in 

 their shape, as to show pretty distinctly that they have been produced 

 by the fusion of others. Originally three cells have existed — two below, 

 and separated from each other, and a third above them, its ends resting 

 on the nearest points of tlie rest. The line of junction has subse- 

 quently become absorbed. In many of the larger hairs a still further 

 absorption has taken place of the partition walls, so that the hair ulti- 

 mately resembles a hollow cylinder, with irregular projections from the 

 central chamber. The intention of this cellulai- formation will be 

 glanced at hereafter, the most obvious is to afford bulk without increase 

 of weight. 



The cellular structure of the hair is best shown by immersing it into 

 turpentine or Canada balsam, whose refracting power, being about the 

 same as that of the hair, deprives it of the dark shadows produced by 

 its convexity, and enables us to examine the interior as if it were flat. 

 The cells, whatever their origin may be, are found usually to contain 

 air, and so are well mapped out by the depth of their shadows ; after 

 the lapse of time, however, the cells are gradually filled by the balsam 

 taking the place of, or absorbing the air, and the whole becomes trans- 

 parent. When filled, we find that there are a number of transverse 

 lines or planes occupying the interior walls of the cells, which vary in 

 colour, according to the colour of the fur of the animal, but usually 

 consist of carbon in a minute state of sub-division. This is pai'ticularly 

 well seen in the hairs of the mole, and in the darkest ones of the rat 

 and mouse. This colour receives its utmost development in black wool, 

 in which the carbonaceous matter is deposited on all the walls of the 

 cell, so as to give the appearance of a large black patch instead of a 

 single plain surface. 



The deposit of pigment in the medullary cell is very marked in many 

 large hairs, such as those of the ichneumon, lion, and sable. In them 

 the amount is so great as to give the central portion the appearance of a 

 perfectly black canal, and the difficulty of even tracing the cell walls is 

 80 great, in consequence of their obscurity, that many observers have 

 been inclined to hold the opinion, that the centre of the hair was occu- 

 pied by a tube, lined by a hypothetical membrane. A patient boiling in 

 turpentine will suffice to fill the cells with this fluid ; they then become 

 transparent, and we can see not only the cellular character of the struc- 

 ture, but also the mode in which the colour granules are deposited. 



