1866.] resembling Quinine, in Animals, ^c. 75 



The colour of the light dispersed through the retina is greenish white, 

 very different from that which the direct perception of these rays usually 

 gives. 



In 1858, in the Comptes Rendus des Seances de la Societe de Biologic 

 pendant le mois de Novembre 1858, pp. 166 & 167, there is a short 

 notice headed " Analyse et conclusions d'un travail sur la fluorescence des 

 milieux de I'ceil, par M. Jules Regnauld." 



He used sunlight, and found in man and the mammifera that the cornea 

 fluoresced in a very slight degree. In the sheep, dog, cat, and rabbit, the 

 crystalline lens possessed in the highest degree fluorescent properties. In 

 these animals, and also in many birds, the central part of the lens (endo- 

 phaine of MM. Valenciennes and Fremy), preserved by desiccation at a 

 low temperature, retained this property. 



The central portion of the crystalline of many aquatic vertebrata and 

 mollusca (phaconine of MM. Valenciennes and Fremy) is almost entirely 

 without fluorescence. 



The hyaloid body possesses only a very feeble fluorescence, due to the 

 hyaline membranes ; for the vitreous humour itself is not fluorescent. 



The retina, as M. Helmholtz discovered, possesses a certain fluorescence 

 which is not at all comparable in intensity to that of the crystalline lens of 

 mammifera. 



Finally, M. Regnauld concludes that, if we must attribute the accidents 

 caused by feebly luminous radiations of the electric light to the phenomena 

 of fluorescence, it is above all in the energetic action on the crystalline that 

 it is natural to look for an explanation. The impression which the cornea 

 undergoes must nevertheless not be neglected. 



In 1859, in the * Archiv fiir Ophthalmologie,' vol. v. part 11. p. 205, 

 there is a paper by J. Setschenow of Moscow, On the Fluorescence of the 

 Transparent Media of the Eyes of Man and some other Animals.'* He 

 undertook the examination at Professor Helmholtz's request, because it was 

 possible that the phenomena of fluorescence observed by Helmholtz might 

 have been modified by a post-mortem change in the eye. 



He experimented on the eyes of oxen and rabbits. The fresh retina 

 showed the same phenomena as the dead human retina. It difl'used a 

 greenish-white light, which, examined by a prism, gives a spectrum in which 

 the red is wanting. 



The vitreous humour in a thin glass vessel showed only traces of fluo- 

 rescence. The lens, on the contrary, fluoresced very strongly : the colour of 

 the dispersed light is white-blue, exactly like quinine ; only the quinine was 

 a little stronger. Examined by a prism, the dispersed light gave a spectrum 

 in which the red was wanting, and in which the blue tone predominated. 

 The fluorescence begins, as in quinine solutions, between G and H, and is 

 strongest at the outer edge of the violet rays, and extends into the ultra- 

 violet to the same distance in the case of the lens as in the case of the 

 quinine solution. 



