Ieb. I, 1865. J 



SCIENCE-GOSSIP. 



29 



resolving the difficult markings on some of 

 the finer forms Ol Diatoraacece, to a future op- 

 portuuitj. J. S. 



A CHAPTER ON HAIRS. 



AMONGST the numerous subjects v/hich 

 animal products supply for the worker 

 with the microscope, there are few which ai'e 

 more interesting, or which offer a greater 

 variety of structure, than those delicate fila- 

 mentous processes which constitute the sub- 

 stance we know as hair. To pluck out a hair 

 froQi the head of a playmate, and look at it 

 with a simple microscope, is one of the first 

 experiments of schoolboy days, although the 

 result of the investigation is not always satis- 

 factory, for reasons which will be presently 

 appax'ent. Although this epidermal substance 

 is not confined to hair only, but under various 

 circumstances takes the form of horn, hoof, 

 and nail, yet, as an external appendage, haii's 

 are found not only on the superior orders of 

 animals, but are likewise developed on the 

 lower orders, on various insects, and to a 

 limited extent on crustaceous animals ; hence 

 it naturally follows that the variety of hair is 

 very great, its limits not being confined to the 

 quills of the porcu[>ine on the one hand, or 

 the delicate hairs of the butterfly on the 

 other ; examination having proved that the 

 horn of the rhinoceros is but a mass of hairs 

 firmly united together, while the revelations 

 of the microscope render it difficult to say 

 how small those hairs may be which the in- 

 sect world possesses. 



It will be sufficient for our present purpose 

 to refer more particularly to hair as conimonly 

 understood, and we may accept as a type of 

 it, that with which v/c ai'e most familiar, viz., 

 human hair. This substance originates in a 



Eig. 1. — Human Hair. 



bulbous root, contained in a depression of the 

 skin, termed a "hair-follicle," and it is by an 

 accumulation of the pulp within the bulb, that 

 the hair is formed and in due course pushed 



upwards. When viewed through a micro- 

 scope with reflected light, the external cover- 

 ing only is seen, which is called the cuticle, 

 and consists of a thin membranous substance, 

 freely marked with irregular lines, which 

 result from the imbricated edges of scales or 

 compressed cells v/ith which the shaft is en- 

 veloped (fig. 1). 



When viewed with transmitted light, a 

 dark line is seen to run up the centre, which 

 for a long time sustained the notion that 

 human hair was tubular. A more careful 

 investigation, however, has shown that the 

 dark line is due to air, contained in cells, 

 forming a pith or medullary substance. Sur- 

 rounding this central column, and forming 

 the bulk of the hair, is a fibrous substance 

 termed the cortex, which, like the medulla, 

 consists of cells, and to this horny portion of 

 the hair is due its peculiar properties of 

 strength and elasticity. There are likewise 

 a number of pigment granules, exceedingly 

 small, but which give to hair its various 

 shades of colour, according as they are more 

 or less numerous. 



The microscopist will find a never ending- 

 variety in the structure of hair, both with 

 regard to the internal and extei'nal arrange- 

 ments of the scales, cells, and pigment. Thus, 

 v/hile human hair is comparatively smooth, 

 the hairs of many animals are rough, and the 

 scales on their sur-face looser. This is a prin- 

 cipal reason why vs'ools are so useful fur 

 weaving and felting, processes for which 

 human hair is not applicable. A reference 



Eig. 2.— East India "\Yool. 



to figs. 1, 2, and 3 will illustrate the difference 

 between human hair and wool, which is but 

 a modification of hair, and will explain why 

 Merino wool is so esteemed by the manufac- 

 turers. 



The v^ool of some kinds of goats, termed 

 mohair (tig. 4), is of a similar character, but 

 much finer in substance. The hair of the 

 bat tribe affords most interesting objects, 

 from the peculiar arrangement of the cortical 

 scales, which project very much from the 



