302 A MANUAL OF VETERINARY PHYSIOLOGY 



tain vortices seldom absent^; one, the largest, may generally 

 be seen in the flank; the hair over the loins distinctly divides 

 as it approaches the crest of the ilium, one current passing 

 over the quarters, another down the flank. This is met by a 

 stream passing up the flank, which divides the hair right and 

 left ; on the left (if the near side be inspected) it passes forward 

 and downwards over the flank, on the right it curves outwards 

 to pass down the quarters. Another vortex may often be seen 

 issuing from under the belly, just in front of the flank, and 

 radiating upwards. The neck, just below the angle of the jaw, 

 has also a vortex, and there is one on the face ; but there are 

 many others not so regular though frequently seen — for instance, 

 on the poll, on either side of the neck, middle line of the neck, 

 over the pectoral muscles, stifles and diffuse areas below the 

 knees and hocks. In Fig. 91 the general direction of the body 

 hair has been indicated. ' Feather ' was the very apt term 

 applied a century ago to the hair pattern of which we are speaking. 

 In the present day feather is employed to designate the hair on 

 the legs of cart horses, so that the term vortex, employed by the 

 Germans, is adopted. It must, however, be remembered that 

 though vortex suggests a circular pattern, many are elongated 

 and distinctly ' feather like.' 



Of the pigment in hair which gives colour to the coat, our 

 knowledge, until quite recently, has been of the scantiest kind. 

 The active investigation now being carried out of Mendel's 

 theories of heredity, when applied to the special case of heredity 

 in coat-colour, made it essential to know more about the origin, 

 nature, and behaviour of the hair pigments, and so we now 

 have some information which is both interesting and promising.* 

 Using the name in its generic sense, three different forms of 

 ' melanin ' are found in hairs — black, chocolate, and yellow. 

 Of these the black is extremely insoluble, and hence very difficult 

 to deal with ; as also is the chocolate pigment, though to a less 

 extent. The yellow, on the other hand, dissolves readily in 

 numerous solvents, and may thus be easily obtained. In its 

 reactions it differs entirely from the black and chocolate pig- 

 ments. In the case of mice there is now no doubt that their 

 varying colours are due to the presence in their hairs of one or 

 more of these three pigments. The less numerous experiments 

 so far made with horse-hairs, suggest no doubt as to the different 

 colours of horses being due to causes essentially the same as those 

 which give the various colours to mice. As to the origin oi 

 these pigments, it has generally been presumed that they must 

 be derivatives of haemoglobin, but there are no pathological or 

 purely chemical facts in definite support of this view. On the 

 * Florence M. Durham (Proe. Roy. Soc., vol. Ixxiv., p. 310, 1904). 



