356 



SCIENCE 



[N. S. Vol. LIV. No. 1398 



professor of eugenics in the child-welfare re- 

 search station of the State University of Iowa. 



Dr. Ealph F. Shanee, for several years 

 connected with the department of anatomy of 

 the Harvard Medical School, has entered on 

 his work as assistant professor of anatomy in 

 the University of Alberta. 



Dr. D. Burns, Grieve lecturer on physio- 

 logical chemistry in the University of Glas- 

 gow, has been appointed professor of physi- 

 ology in the University of Durham College of 

 Medicine, Newcastle-upon-Tyne, in succes- 

 sion to the late Professor J. A. Menzies. 



DISCUSSION AND CORRESPONDENCE 



THE CAUSES OF WHITENESS IN HAIR AND 

 FEATHERS 



My attention has recently been called to a 

 statement by W.D. Bancroft^ to the effect that 

 white hair and feathers owe their color to the 

 entrance of air into their structure. Similar 

 statements have appeared elsewhere at vari- 

 ous times, and this conception appears to be 

 widespread. 



No one, to my knowledge, has ever present- 

 ed any real evidence that either hair or 

 feathers have any more air in them when 

 white, than when colored. Furthermore it 

 is quite unnecessary for them to have more 

 air. I have never been able to see any 

 difference in the structure of white hair and 

 feathers as compared with colored hair and 

 feathers, except for the presence or absence 

 of pigment. 



In 1904, I made the statement, in an ad- 

 dress, that hair and feathers are white for 

 the same reason that ipowdered ice or glass 

 and other transparent substances in a fine 

 state of division appear white.^ 



Hair consists of numerous cornified epi- 

 thelial cells more or less incompletely fused 

 together. In the case of human hair, most 

 of the structure is cortical. These cells 

 furnish a vast number of external and in- 



1 Applied Colloid Chemistry, 1921, p. 198. 



2 See abstract in Biol. Bull., 1904, Vol. VI., No. 

 6, p. 311, for remarks about white feathers. See 

 also Anat. Rec, 1918, No. 1, p. 52, for discussion 

 of white hair. 



ternal reflecting surfaces, as can be seen 

 easily by placing a white hair on the micro- 

 scope stage with no mounting fluid. When 

 pigment is present, the incident light is more 

 or less extensively absorbed, according to the 

 amount of pigment, before reaching the deeper 

 cells. The amount of undispersed light re- 

 flected, of course depends on the number of 

 internal reflecting surfaces not screened by 

 pigment. There is always some reflection of 

 undispersed light by the hair cuticle, no 

 matter how much pigment is present. 



The white of feathers is produced mostly 

 by the barbules which are of microscopic 

 size and consist of single columns of cells. 



Hair and feathers have many times the 

 surface, external and internal, provided by 

 small bodies of similar mass but less intricate 

 structure. According to a well-known law, 

 the surface of a cube varies relatively to the 

 volume inversely as the diameter. Thus a 

 cuboidal cell one tenth of a millimeter in 

 diameter has ten times as much surface, rela- 

 tively, as a body one millimeter in diameter. 

 Furthermore, the amount of reflecting surface 

 is increased by the irregular contour of the 

 hair and feather elements. The total area of 

 the vast number of facets in a single, unpig- 

 mented hair or feather which are in a posi- 

 tion to reflect light to the eye is relatively 

 very great. 



White in hair and feather structures is due 

 to failure or absence of pigment formation in 

 the follicle before cornification takes place. 

 I know of no critical evidence that either 

 hair or feather structure can become white in 

 any other way. The process is therefore slow, 

 and the time required for a change to white 

 is determined by the rate of growth. 



Similar views are expressed in an article 

 by Stieda^ where a discussion of the origin 

 of the notion that hair may suddenly become 

 white is discussed in detail. 



E. M. Strong 



Loyola University School of Medicine, 

 Chicago, III. 



3 Verh. der Gesellsch. Deutscher Naturforsch. 

 und Aerzte., 1910, Bd. 81, 8. 222-224; also Anat. 

 Hefte, 1910, Bd. 40, H. 2. 



