54 The Microscope. 



hairs of such different sizes ? But this is never asked 

 till the first great puzzle is in some sort got over, as 

 to the curious running patterns, resembling a sort of 

 jointed chain in the larger hairs, and a simple row of 

 beads in the smaller. Let us therefore now study them 

 in the light of the remarks lately made on the structure 

 of hair, how that it generally consists of a cortical or 

 investing substance, of a dense horny texture, and a 

 medullary or pith-like substance, usually much softer, 

 and occupying the interior. Now in the hair of the 

 white mouse both can be very well seen j the apparent 

 glass rods are the cortical substance or rind of the 

 hair, and the chain-like patterns which they enclose 

 are the medullary substance or pith. This consists 

 entirely of cells, which vary in shape and arrangement 

 in the hairs of different animals. In the mouse you 

 see they are large and distinct, and arranged in rows. 

 In some hairs of the rabbit they lie like the grains on 

 an ear of Indian corn. In the cat they are closely laid 

 together, and this is the case also with the otter ; but 

 at this object I imagine you will pause and inquire, 

 "What is this scale-like appearance on the otter's 

 hair ? " and in reply I ask you to remember that 

 "all animal and vegetable structures are developed 

 from cells," and that the rind or cortical substance 

 of hairs has been formed by a succession of cells, 

 which at its surface become flattened into scales as 

 the hair grows. 



The otter's hair shows this scaly structure to great 

 advantage. 



The internal cells of the mouse's hair show in a 



