The hair of the cat has a superficial resemblance to that of the thinner hairs of the rabbit. The medullary canal is very prominent, and occupies more than half of the fibre. It is made up of a single series of quadrilateral cells, but unlike the cells in rabbit's hair, these may form additional layers in the thicker parts of the hair. The hair is generally a little over half an inch in length, and tapers to a fine point. [Illustration: WOOL FIBRES From different breeds of Sheep _By kind permission of Messrs. Scott Greenwood & Co._ (IRISH WETHER) (NEW ZEALAND) (NORTH HOG) QUEENSLAND SHEEP (LINCOLN WETHER) (ARGENTINE CROSS BREED)] Dog's hair differs from the hair of the cat both in size and appearance. It is about three times as wide, while the medullary canal only occupies about one quarter of the diameter of the fibre. The surface of the hair is covered with characteristic scales, the edges of which project, so that the edge of the fibre has a saw-like appearance. The accompanying plate shows hair taken from a Pekin spaniel and Persian kitten, and drawn to the same scale of magnification (104 diameters). In the hair of the kangaroo the serrated edge of the fibres, due to projecting scales, is much more pronounced than in dog's hair. The medulla is well marked, but lacks the cellular structure to be seen in the hair of the cat and rabbit. Goat's hair could not possibly be mistaken for human hair under the microscope. It has a root of characteristic appearance, and shows a well-marked medulla containing a structure of narrow cells. Towards the middle the hair becomes very narrow, but expands again and reaches its greatest diameter a little before the point. Sheep's wool is characterised by its surface structure of scales, the arrangement of which differs in the wool from different breeds of sheep. In some of the fibres the medullary canal is very manifest. Typical fibres of sheep's wool are shown in the figures. It is often necessary to distinguish between fabrics of cotton, linen, silk and wool, and in such cases the microscopical appearance of the fibres is invaluable as a preliminary test. Cotton is characterised by its curious corkscrew-like twists, and linen by its jointed structure, while silk has a long smooth cylindrical fibre, devoid of scales and showing little sign of structural formation. In criminal cases neither cotton nor silk are likely to be claimed as human hair, although one may easily conceive the possibility of occasions arising where the composition of a peculiar material was a point of the utmost importance. [Illustration: COTTON FIBRES] [Illustration: FLAX FIBRES _By kind permission of Messrs. Scott Greenwood & Co._] CHAPTER XIII EARLY POISONING TRIALS Murder of Sir T. Overbury--Mary Blandy--Katherine Nairn