F. A. E. Crew 167 



and with, different methods of illumination, these scales, witli their free 

 edges typically directed towards the tip of the hair, could not be found 

 until the heavily pigmented very small hairs from the summer coat were 

 examined. 



In the longer and older hairs the cuticle had disappeared (PI. II, 

 Fig. 4), probably by attrition during life, leaving the cortical cells ex- 

 posed, and only near the bases of such hairs could remnants of the cuticle 

 be found. In the case of the shorter and younger hairs the cuticle had 

 been preserved since these hairs had been amply protected by the longer 

 ones (PI. II, Fig. 5). 



The hair fibres were never entangled, and naturally do not felt as 

 they are too straight, too stout, and too up-standing, and in the case 

 of the young hairs upon which the cuticle is still present, the cuticular 

 scales have free edges which are not serrated. 



Figs. 2 and 3 show that the disposition of the pigment granules of a 

 hair is such that they outline the cells of the cortex. It was found that 

 when a winter white hair was mounted in weak balsam it assumed the 

 coloration of a pigmented summer hair. This was possibly due to the 

 withdrawal of air as the following experiment shows. A white hair, 

 mounted in weak balsam and examined under the microscope, was sub- 

 jected to gentle pressure along its length by means of a pencil-point. 

 The hair ruptured, and air-bubbles rushed out, leaving the fibre pig- 

 mented. On removing the pressure the air rushed back and the hair 

 became once more white. 



The medulla of a hair could not be seen through the cortex, but 

 it seemed that the spaces of the medulla were occupied by air which 

 made its way among the cortical cells. If air comes to he between 

 the pigment of the cortex and the eye of an observer, the refractive 

 properties of the air-film render the pigment invisible. The presence 

 of air within a hair is associated with age: a white hair is an old 

 hair. The air-film, moreover, gives a heat-retaining property to the 

 outer coat and incidentally provides a protective coloration. It was 

 found that the air-film prevented aqueous dyes from entering the 

 fibres. It is suggested that kemp is such a fibre, a hair prematurely 

 old. 



The Wool. The wool fibre has the same essential histological structure 

 as a hair save that it is finer — 0-1 of the diameter of a hair — non- 

 pigmented, and has many more waves to the inch. It is so constructed 

 that it is impossible to distinguish between cuticles and cortex. One 

 cell with free edges serrated and projecting towards the tip, occupies 



Ann. Biol. ViJI 12 



