1 68 Hair in its Microscopical and Mtdico-Legal Aspects. 



striped appearance alone shows the cellular structure. Concen- 

 trated sulphuric acid breaks up this union, and reveals the spindle- 

 shaped cells, with occasionally a nucleus. 



The cortical substance has different colour, according to the 

 colour of the hair ; generally the colour is diffused through its 

 whole mass; less frequently the colour depends on granular pig- 

 ment scattered through its substance in small masses. 



Finally, the cortical substance contains a number of cavities 

 filled with air, most evident in the hair from aged persons or in 

 dry hair. These are secondary results of drying, as they are not 

 found in young hair. 



The central portion, the medullary substance, forms, when well 

 developed, an axis-cylinder, one-fifth or one-fourth the diameter of 

 the hair, with sharp outlines, generally central, but many times a 

 little eccentric in position. The medullary substance is not con- 

 stant ; it is often wanting in human hair, especially in blond hair. 

 It is wanting less frequently in hair obtained from other parts of 

 the body than in that from the head. In woolly hair it is always 

 wanting ; also in the hair of the new-born child. The medullary 

 substance is often interrupted, and sometimes consists only of a few 

 dark points lying in the axis of the hair. 



The nature of the medullary substance is still a matter of dis- 

 pute, some considering it cellular, others denying this. The first is 

 certainly the correct view, as may be seen by following the develop- 

 ment of the medullary substance from the papilla, where round and 

 imperfectly-polygonal cells can be seen gradually merging into the 

 medullary substance. 



The medullary substance has been thought to contain the pig- 

 ment ; this is not so, the supposed pigment-granules being very 

 minute air- bubbles. The cause of the colour of the hair is found 

 in the diffuse pigmentation of the cortical substance. The cause 

 for the hair becoming grey or white is to be found in the disappear- 

 ance of the diffuse pigmentation of the cortical substance, the cause 

 of which is not yet known. The medullary substance can be more 

 easily seen in white hair than in coloured. 



Turning now to the hair of animals, we find generally the same 

 three layers as in human hair, but differing to such a degree that, 

 as a rule, a hair can be easily recognized as belonging to an animal. 

 The cuticula in most animals has absolutely and relatively larger 

 cells, which give the hair a characteristic appearance, as is seen 

 especially well in the wool from sheep. A toothed or -saw-like ap- 

 pearance of the contour of certain animal hairs depends upon the 

 larger development and peculiar relations of the cuticular cells, 

 whose points stand out so far from the hair that the latter has a 

 feathered appearance, as in the field-mouse. Among animals the 

 greater bulk of the hair is formed by the medullary substance, the 



