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[Page 293]
(Reprinted from NATURE, March 19, 1927.)
THE COAT OF SHEEP
IN an important work, "Das Haarlleid des Menschen," published in 1908, Dr. Hans Friedenthal points out (1) that in man the coat between the fourth and fifth month of development consists entirely of fine wool fibres, and (2) that shortly before birth there appear among the fine wool fibres strong pigmented fibres with a pith or medulla, i.e. fibres corresponding to the coarse fibres forming the outer coat of wild sheep. Hitherto it has been assumed that the simple pithless fibres forming the coat of the Merino and other fine-wooled sheep are modified true hair fibres - hair fibres that have lost their medulla, from which, according to Bowman (the author of the standard work on wool), "the medulla has been bred out." From an investigation which has been in hand for some time on the structure of the fibres forming the coat of the sheep, it has been ascertained that in sheep, as in man, the first coat consists entirely of simple pithless fine wool fibres.
In the case of sheep, the gestation period lasts about twenty-two weeks. Though at the end of the twelfth week of development there are only a few fibres on the lips and at the tip of the tail, there is a complete coat at about the end of the fourteenth week. The fibres forming the first coat vary in length. In some areas they are so short that they are inconspicuous, in others they are nearly a quarter of of an inch in length. The long fibres in sheep at the end of the fourteenth week, like the long eyebrow fibres in the human embryo, are obviously wool fibres. Though up to the middle of the fifteenth week the coat consists entirely of fine pithless wool fibres, at the end of the fifteenth week, more especially in the embryos of Highland Blackface and other coarse-wooled breeds, short coarse true-hair fibres with an interrupted or a continuous medulla are found among the fine wool fibres of the first coat. As the development proceeds the coarse medulated fibres increase in number, and even in some fine-wooled breeds attempt to form an outer coat. In Europeans, as Friedenthal points out, there is, even in old age, usually a vestige of the first coat of wool.
In all wild sheep there is during winter a complete inner coat of very fine wool and an outer coat of coarse hair. Even in present-day domestic fine-wooled breeds there is always, on the head and limbs, a remnant of the original ancestral outer coat of coarse hair.
From this short account of the investigations in hand, it follows that a study of the coat of sheep during fœtal life lends no support to the view hitherto held by Bowman and others that wool is hair from which the pith or medulla has been bred out, but shows that wool is a distinct and primitive type of fibre different alike from fur and hair.
J. COSSAR EWART.
The University, Edinburgh.
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