68 MOSTLY MAMMALS 
“The part played by phagocytes,” writes the author, 
“in the whitening of the hair explains many phenomena 
observed long ago, but not as yet sufficiently understood.” 
Thus the phenomenon of hair turning white in a single 
night, or in a few days, may be explained by the increased 
activity of the phagocytes, which remove the pigment 
within an abnormally short period. 
