156 On the Process of Hair turning White. 



" On the Process of Hair Turning White," By E. METCHNIKOFF, 

 For. Mem. K.S. Eeceived November 7, Read November 

 21, 1901. 



Although the fact of hair turning white is a most familiar one, its 

 mechanism has not as yet been unveiled. The authors of works on 

 hair and dermatology acknowledge their ignorance concerning this 

 subject. 



Having undertaken a study on atrophic processes, and especially on 

 senile atrophy, my attention has been called to the atrophy of hair 

 pigment so frequent in old people. 



Observations on grey hair, or on hair beginning to turn grey, showed 

 me that the atrophy of its pigment is due to the intervention of 

 phagocytes of the hair. 



These cells have a single nucleus and their very different aspect one 

 from another is due to numerous amoeboid prolongations of their 

 protoplasm. They are derived from the medullary part of the hair 

 and make their way out into its cortical layer, where they absorb the 

 pigment granules, which they then remove from the hair. 



If we consider hair, one part of which is already white and the 

 other still pigmented, we find a great many of these phagocytes. 

 They are supplied with greatly developed prolongations and become 

 insinuated between the keratic cells of the peripheral layer. 



In absolutely white hair the phagocytes filled with pigment become 

 more and more scarce, and most frequently completely disappear. 



It is thus indubitable that the phagocytes of the hairs swallow up 

 the granular pigment of the cortical layer and transfer it elsewhere, 

 the result being the complete whitening of such hair. On observing 

 the root of hair beginning to whiten, we often find a great many 

 phagocytes filled with pigment. 



The whitening of the hair of old dogs proceeds by the same 

 mechanism. We equally find here a great number of phagocytes 

 supplied with numerous prolongations and stuffed with pigment 

 granules. 



The part played by phagocytes in the whitening of hair explains 

 many phenomena observed long ago, but not as yet sufficiently 

 understood. Thus, hair turning white in a single night, or in a few 

 days, may be explained by the increased activity of hair phagocytes 

 thus enabled to transfer the pigment in so short a time. 



The mechanism of the whitening of hair through the agency of 

 phagocytes, allows this case of atrophy to be classed under the general 

 laws of atrophy of solid parts of the organism. 



