512 MEMOIR OF GEORGE WILSON. 



in which he showed the presence of fluoride of calcium, not only 

 in the bones and teeth, but in the blood, milk, and other secre- 

 tions of recent animals ; then he traced it back to the vegetable 

 world, finding it in the stems of many of those plants which the 

 mammalia use for food. Attacking the question, How does the 

 plant derive its supply of this element ? he found the fluoride of 

 calcium soluble to a slight extent even in pure water, and occur- 

 ring not merely in the mineral fluor spar itself, but also in 

 small quantities in granite, porphyry, and many other rocks. 

 He found it to be dissolved by the springs, and thus what is 

 not absorbed by the plants feeding on the soil makes its way 

 into the rivers, and ultimately into the sea, among the salts 

 of which fluorine was discovered to be an ordinary constituent. 

 Dr. Wilson was led to the conclusion that the fluoride found 

 in some of these big bones of ancient times had filtered into 

 them, forming a very insoluble compound with the phosphate 

 of lime. 



Dr. Wilson's researches on Colour- Blindness appear to me the 

 most complete of his investigations, and those with which his 

 name will be most inseparably associated. In November 1853 

 he commenced a series of papers in the ' Edinburgh Monthly 

 Journal of Medical Science' on Colour-Blindness, or Chromato- 

 pseudopsis, as he termed it. During this investigation, he not 

 merely brought together the substance of everything that had 

 been previously written on the subject, but he collected accounts 

 of all the colour-blind whom he could induce to describe their 

 peculiarities faithfully in writing, or to let him examine them. 

 There were tailors who matched a scarlet waistcoat with green 

 strings ; clerks who signed their names in red instead of black 

 ink ; physicians who never saw the tint of their patients' com- 

 plexions ; and laboratory students who were never sure of the 



and on the presence of Fluorine in Granite, Trap, and other Igneous Rocks, and in 

 the Ashes of recent and fossil Plants. ' Trans. R. S. E.,' vol. xx. part iii. 



On the Extent to which Fluoride of Calcium is Soluble in Water at 60 F. ' Trans. 

 Brit. Assoc.' 1847, p. 61. 



On the Presence of Fluorine in the Stems of Graminea;, Equisitaceai, and other 

 Plants, with Observations on the Sources from which Vegetables derive this clement. 

 <Bot. Soc. Edin.' 1852. 



On M. J. Nickle's Claim to be the Discoverer of Fluorine in the Blood.- 'Phil. 

 Ma*,'.' March 1857. 



