76 



Messrs. Jones and Dupre on a Substance, [Apr. 12, 



When the cornea was cut out, it fluoresced much feebler than the lens ; 

 the aqueous humour did not fluoresce at all. 



The appearances in the three last media, he says, can be shown Avith 

 the greatest ease, even in the eye of a living man. When the eye is brought 

 into the focus of the ultra-violet rays, immediately the cornea and the lens 

 begin to glimmer with a white-blue light. The cornea in the living eye is 

 much more strongly fluorescent than when dissected out, probably from 

 the loss of transparency consequent on contraction of the texture and from 

 evaporation. 



The question how and why our eyes perceive the ultra-violet spectrum 

 is still undetermined. The fluorescence of the lens would be rather a 

 hindrance than a help ; only the general sensibility to the light which the 

 ultra-violet rays produce in our eyes can be explained by the fluorescence 

 of the media lying before the retina. 



In 1862, ' Zeitschrift flir Rationelle Medicin,' 3rd series, vol. xiii. p. 270, 

 Pfluger, by mixing fresh ox- gall with concentrated sulphuric acid, saw a 

 clear dichrotic solution form. It had a deep red colour by transmitted 

 light, and a beautiful green colour by reflected light. This was seen 

 very beautifully when dried bile was put into sulphuric acid ; and then the 

 dichroism increased by standing. It is desirable to separate the choles- 

 terin and the bile-fats. 



The green fluorescence appeared when only blue or green light fell on 

 the sulphuric-acid solution of the bile. On the contrary, it did not appear 

 when the light v^^as only yellow or red. 



The sulphuric-acid solution of the bile absorbed all the rays of the spec- 

 trum except the yellow and the red. 



In the * Journal fiirPrakt. Chem.' vol. xcii. p. 167, Schonbein has the fol- 

 lowing remarks on the formation of a fluorescing substance in the putrefac- 

 tion of human urine : — 



If urine is left to stand in the air until it becomes covered on the 

 surface with a thick layer of fungus, the alkaline fluid that filters from 

 it shows a very strong fluorescence of a greenish colour. Small quanti- 

 ties of the stronger organic or inorganic acids take away this fluorescence, 

 which, however, by alkalies can be again reproduced. This substance 

 has a reaction like esculine, and, like this, is the opposite to quinine, the 

 fluorescence of which is increased by those acids. The hydrobromic, 

 hydriodic, and hydrochloric acids lessen the fluorescence of the solution of 

 quinine almost to entire removal. Schonbein also remarked that fresh 

 urine had a feeble fluorescence, and also that a weak solution of albumen, 

 by standing long in the air, became fluorescent to a considerable degree. 



This was the state of our knowledge of fluorescence in animals when, 

 having traced the rate of passage of chloride of lithium and other mineral 

 substances into and out of the textures by means of the spectrum analysis, 

 we endeavoured to find some method of determining the rate at which 

 organic substances passed into and out of the same structures. 



