THE HAIRS OF ANIMALS. 



By C. AINSWORTH MITCHELL, B.A. (Oxon), F.I.C., and R. MORRIS PRIDEAUX, F.I.C. 



The study of the hairs of animals has been singu- 

 larly neglected, notwithstanding the many questions 

 of scientific interest that it involves. With the 

 exception of silk and wool, which now have a fairly- 

 full literature of their own, little will be found in 

 textbooks about other animal fibres and the curious 

 differences in structure shown by the hairs of 

 different species of animals. In the present article, 

 therefore, we wish to give a general outline of the 

 nature of hair, together with some account of 

 observations that have been made by us and not 

 hitherto published. 



In the popular view, wool and hair are usually 

 regarded as something quite distinct, but the 

 difference is one of degree rather than of kind. 

 Wool may be defined as a particular variety of hair 

 of fine texture characterised by having a more or 

 less curled form and a surface covered with scales 

 which tend to overlap each other. As a rule there 

 is no medulla. 



This distinction between hair and wool is by no 

 means sharp, and it is not uncommon to find the 

 same animal producing both types of fibres. For 

 example, in trie hair of the goat there is a lower 

 layer of woolly fibres, and a similar mixture of the 

 two sorts of fibre may be observed in the coats of 

 certain breeds of dogs, such as the Bedlington 

 terrier (Figure 299). 



In the case of the Siberian sheep the nature of 

 the hair varies with the seasons, the coat being of a 

 hairy type in the summer, but changing to wool in 

 the winter. The predominance of woolly fibres in 

 the coats of ordinary breeds of sheep is largely the 

 result of the animals having been kept for generations 

 under exceptional conditions, and of special breeding 

 to produce this result. When the ordinary domestic 

 sheep is allowed to run wild, it will in the course of 

 a generation or so produce a fleece containing a 

 large proportion of straight fibres. 



The character of the scaling upon wool is an 

 important factor for distinguishing between the 

 products of different breeds. For example, in the 

 wool from the merino sheep, the scales go round the 

 fibre, so that the microscopic appearance suggests 

 that of a Malacca cane, with closely set joints (see 

 Figure 295), whereas in the wool from cross-bred 

 sheep the scales are smaller and cover only a small 

 section of the axis of the fibre (see Figure 296). In 

 healthy wool the scales cover the area of the fibre 

 completely, but in certain diseased conditions the 

 cortex will appear bare in patches. It is not 

 uncommon, however, to find in the wool of lambs 



that have not yet been shorn numerous fibres from 

 the tips of which the scales have been completely 

 stripped by friction (see Figure 297). 



The scales on the hair of animals are best 

 examined by oblique illumination by throwing the 

 iris diaphragm out of the optical axis of the instru- 

 ment. This causes the projecting edges of the 

 scales to catch the light in such a way that they 

 stand out clearly. 



The number of scales on a given area varies 

 greatly. For example, Hanausek found that in one 

 millimetre length the number of scales showed the 

 following variations :— 



The cortex or surface beneath the scales frequently 

 shows longitudinal streaks, and in the coarser types 

 of hair a medulla or central canal may be present. 

 This medulla may be continuous along the length of 

 the fibre, or it may show interruptions in places, or 

 stop abruptly. It often shows cells of characteristic 

 form, while in other cases it is made up of granular 

 particles. It is best examined under the microscope, 

 with the iris diaphragm reduced to a small aperture. 



Frequently it will be found that when both 

 woolly and hair-like fibres are produced by the 

 same animal, the former show no indications of a 

 medulla, whereas the latter have a pronounced 

 medulla. A good instance of this may be seen 

 in the hair of the Cashmere goat and in that 

 of some of the small American goats. In vicuna 

 fibres from Auchenia vicuna, fine woolly hairs with- 

 out medulla predominate, whereas in alpaca hair 

 from Auchenia paco most of the fibres are coarse 

 and show a medulla. 



The wavy structure of woolly hairs, which is 

 most pronounced in the finest varieties of sheep's 

 wool, appears to be due to contractions, which are 

 caused by the cells upon the cortex being uneven. 

 In types of wool which approximate more nearly to 

 hair, as, for example, that of the Angora goat or 

 mohair, there is only a slight tendency' towards 

 curling. 



Another point to which attention must be given 

 in differentiating the fibres of different species of 

 animals is the distribution of the pigment in the 

 cortex. In studying this feature under the micro- 

 scope as much light as possible should be transmitted 

 through the fibres. This will cause all signs of 



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