THE VARIOUS LAYERS 149 



to melanin. There seem to be several varieties 

 of this pigment. Compared with the hairs of 

 other animals the melanin of the human hair 

 contains less nitrogen and more sulphur.' * 



As to the physiological composition of a 

 single hair, we have the medulla in centre ; 

 this is surrounded by the cortex; next in 

 order is the cuticle, then Huxley's layer; 

 Henle's layer is next ; then we have the 

 external root sheath; next in order is the 

 homogeneous layer ; outside this the layer of 

 circular fibres ; and next the layer of horizontal 

 fibres. The three latter make up the connective 

 tissue portion of the hair follicle, t 



We have roughly enumerated merely the main 

 facts connected with the component parts of a 

 hair ; and although we have omitted the relative 

 functions of all these parts, we must agree that 

 a hair is a most wonderful structure. 



But we have not yet done justice to the hair. 



* Text- Book of Human Physiology. Landois and Stirling. 

 (C. Griffin & Co.) 



t Text-Book of Physiology. McKendrick. (J. Maclehose 

 & Sons.) 



