OF THE CLASS MAMMALIA. 237 



tube, filled with a pulpy matter. They vary in form, being 

 in most animals cylindrical, and .larger at their base than at 

 their summit ; in others more or less flattened or lamellated, 

 like sprigs of grass; sometimes their surface is smooth, 

 sometimes roughened with asperities, or having a moniliform 

 aspect ; finally, they differ in form and elasticity, not only in 

 different animals, but even in different parts of the same 

 animal. 



From these circumstances, the names given the hairs differ, 

 being called barbs, or quills, or bristles, or simply hair. Wool 

 is a sort of hair, very long and tortuous ; fur is a still finer 

 form of hair concealed beneath a covering of ordinary hair. 



The colour of the hair, which varies so much, may yet be 

 referred to modifications of white, black, brown-red, and 

 yellowish ; it seems to depend on the presence of a coloured 

 fat, soluble in boiling spirits of wine ; when this is extracted 

 by the action of the above solvent, the hair becomes of a 

 greyish yellow colour. In white hair a white-coloured oil 

 is found, and in red hair, oil of a reddish colour ; in black 

 hair a blackish oil, somewhat blue, from the presence of sul- 

 phuret of iron.* Sometimes the hairs have the same colour 

 throughout their whole length ; sometimes they are darker at 

 their base than towards their summits, and sometimes they 

 present a series of white and coloured rings. Moreover, their 

 colour varies much in different parts of the body, and the 

 general disposition of these tints constitutes what is nominally 

 called the fur (pelage). Generally the colours are much 

 darker towards the back, and when there are spots, these are 

 almost always disposed symmetrically on the sides that is, 

 so long as domestication does not exercise its influence, for 

 then the colouring of the robe presents often the greatest 

 irregularity. 



The fur is generally the same in both sexes, and generally 

 varies but little at different ages. Yet in some, the young 

 have spots and a variety of shades, which disappear in the 

 adult, and it not unfrequently happens that the colour of the 

 mammal changes with the seasons. 



Generally the hairs fall annually, in spring time or in 

 autumn, to be replaced by others. This kind of moulting 



* There exists also in different kinds of hair, sulphur, which may readily 

 combine with lead to form coloured sulphurets. It is in this way that the 

 hair may be dyed by the use of leaden combs, or by the application of salts 

 of lead, mercury, &c., the sulphuret which is then formed being of this 

 colour. 



