1867.] of Appearance and Simidure of the Human Hair. 407 



increased perceptibly during the last two years. There is no similar 

 alteration of structure of the eyebrows and eyelashes. His complexion is 

 dark, while that of a younger brother is fair ; and the latter is free from 

 any alteration of the hair. 



Examination of the hair with a lens shows that the cylinder of the hair 

 is perfectly uniform, that the white portion is contained within the cuticle 

 and occupies the whole breadth of the cylinder ; whilst it frequently 

 presents a rounded cone at the central extremity, and breaks up into fibres 

 at the opposite or distal end ; and in some instances this fibrous structure 

 is apparent at both ends of the white segment. Moreover, by transmitted 

 light, the white segment is found to be opake, and consequently presents 

 a dark shade, while the intermediate or brown portion has the transparency 

 of normal hair. 



When the transparency of the hair is increased by immersion in Canada 

 balsam shghtly diluted with spirits of turpentine, the white and opake 

 segment is reduced in dimensions, and is rendered more or less transparent 

 by imbibition of the volatile fluid ; moreover it is clearly demonstrated by 

 this process that the opacity of the segment its whiteness when seen by re- 

 flected light, and its darkness by transmitted hght, are all due to the presence, 

 in the fibrous portion of the hair, of spaces filled with air-globules. The 

 air-spaces are necessarily very numerous and assembled closely together j 

 while at the ends of the white segment they have more or less of a linear 

 arrangement, and give a fibrous appearance to the opake mass. More- 

 over the partial transparency of the hair caused by the balsam demon- 

 strates that, besides the air-spaces, large and small, contained in the opake 

 portion, minute air-spaces, sometimes arranged in linear order, and some- 

 times communicating and forming short irregular canals, are also met 

 with in the transparent part of the hair. And, in addition to the minute 

 air-spaces of the plates of the fibrous portion of the hair, an accumulation 

 of air-globules is also very apparent in the cells of the medulla. 



It is evident from this examination of the hairs, that they are imperfect 

 in structure and development, and that their imperfection indicates a weak 

 producing organ, and probably a weakly constitution of the individual ; that 

 the cells of which the fibrous portion of the hair is composed, instead of 

 being filled with a horny plasma, are tinged with aqueous fluid, and the 

 desiccation of this fluid leaves behind it vacuities which in the subsequent 

 growth of the shaft become filled with air. The most remarkable pheno- 

 menon in connexion with the case, however, is the alternation of imperfect 

 and perfect cells, the period of continuance of the two processes (sup- 

 posing them to be equally active in point of time) being twice as long for 

 the perfect as for the imperfect structure. 



Since the publication of the observations of Berthold in Miiller's *Archiv' 

 for 1850, it is generally believed that the hair grows faster during the day 

 than during the night ; hence the first suggestion that occurred to me in 

 connexion with the present case, seeing that the white or opake segment 



2 L 2 



