1868.] 



Dr. Gladstone on Bcfraciion-Equivalcnts. 



439 



The investigation of this sharply defined strychnine-compound, which 

 can be preserved for months without undergoing any decomposition, goes 

 far to prove the existence of a persulphide of hydrogen, 



1-1,83; 



it is, however, by no means improbable that compounds of hydrogen and 

 sulphur in several proportions may exist. 



The formation of the strychnine-compound which I have described, 

 and which I have often prepared with the same result, could not fail to 

 lead to an examination of several other alkaloids in a similar direction. 

 Quinine, cinchonine, brucine, and several other vegetal bases were re- 

 peatedly submitted to the action of an alcoholic solution of polysulphide 

 of ammonium, but in no case were similar phenomena observed. 



The compound of strychnine with persulphide of hydrogen is remarkable 

 for its insolubihty. An alcoholic solution containing 2-03 grs. of strychnine, 

 when mixed with an alcohoHc solution of polysulphide of ammonium and 

 allowed to stand for twelve hours, was found to have deposited 2-287 grs. 

 of the red crystals, i. e. 87*2 per cent, of the theoretical amount. It 

 deserves to be examined, whether the property possessed by strychnine, of 

 forming so insoluble a compound with persulphide of hydrogen, could not 

 be utilized for the purpose of preparing this alkaloid, and in certain cases 

 even for its detection and separation from other substances with which it 

 might be mixed. 



II. Note on the Anatomy of the Blood-vessel System of the 

 Retina of the Hedgehog." By J. W. Hulke, F.R.S. Re- 

 ceived May 26, 1868. 



(Abstract.) 



This retina is very remarkable for the fact that all the arteries and 

 vehis lie upon the inner surface of the membrana limitans interna retinae, 

 in intimate relation with the membrana hyaloidea ; while capillaries only 

 traverse the limitans, receiving a sheath from it, and penetrate the inner 

 layers of the retina. The hedgehog's retina is in this respect a link be- 

 tween the non-vascular retina of fish, amphibia, reptiles and birds, and 

 the vascular retinae of most mammals. 



III. Researches on Refraction-Equivalents."'^ By J. H. Gladstone, 



Ph.D., F.R.S. Received May 29, 1868. 



Since the paper of the Eev. T. Pelham Dale and myself "On the Re- 

 fraction, Dispersion, and Sensitiveness of Liquids our researches have 

 been continued from time to time, and a good deal of attention has been 

 paid to the subject in Germany. The permanence of the specific refractive 



Philosophical Tran«aclions, 1863, p. 317- 



