PHYSIOLOGICAL 433 



granules in the hair, and carry them off into the skin. Moreover, 

 the replacement of pigment-granules by gas-vacuoles makes the 

 hair white, just as foam is white. In very trying circumstances, 

 a man's hair may turn white very quickly; thus Hrdlicka cites at 

 first hand the case of Greely, the Arctic explorer, whose dark-brown 

 hair became completely white in the course of some months, prob- 

 ably because of the conditions of semi-starvation and great anxiety. 

 Within a year after the explorer's return to civilisation his hair 

 had darkened again, though it never returned entirely to its original 

 chestnut' colour. The sudden blanching of Marie Antoinette's hair is 

 believed to be a historical fact; and there are well-documented 

 cases of a man's hair turning white in a single night. One can hardly 

 suppose that this was due to the activity of wandering chromo- 

 phages; and it is interesting to find that in a case investigated by 

 the physiologist Landois, the pigment was found to be still present, 

 but masked by a profuse production of gas-vacuoles both in the 

 core and the cortex of the hairs. 



It often seems as if the colour of the offspring's hair was a 

 blend of the colours of the two parents; in other cases the children 

 seem all to favour one side of the house. The facts remain inade- 

 quately known; but the probability is that the matter is much 

 more complex than it appears at first sight, as is true in the case 

 of skin colour in mulattos. It is very likely that what we slump 

 under the title "melanin" is a complex of related chemical sub- 

 stances; and we know that a complex coloration, like that of a 

 wild rabbit, may be controlled by several distinct hereditary factors. 

 We get a glimpse of the subtlety of these matters when we find 

 the handing-on through several generations of a triviality like a 

 white forelock, or a particular "crinkliness" in the hair. 



PHAGOCYTOSIS 



One of the most common risks of life — or, we may often say, 

 chances of death — is that of the invasion of the body by microbes, 

 which are in some way or other disintegrative of its healthy unit3^ 

 Many diseases— like cholera, dysentery, plague, and tuberculosis — 

 are due to such invasions by specific bacteria; while others, such 

 as malaria and sleeping sickness, are due to microscopic Prot.o- 

 zoa, not less virulent. They tend to multiply with inconceivable 

 rapidity within the body, for the division of one, even at the hourly 

 rate (often exceeded), would give over sixteen millions in twenty-four 

 hours. So it is no wonder that with such predatory intensity of 

 growth, necessarily accompanied by corresponding formation of 

 waste-products profoundly deranging the life of their victim, they 

 should bring about disease or destruction. In some cases the activity 



VOL. I FF 



