534 Mr. Hermell on Elaierium. 



measure, of alcohol, has been administered in two cases of 

 dropsy, in St. Bartholomew's Hospital, by my friend Mr. Black- 

 more. To a woman, aged forty, labouring under tiscites, ten 

 minims were given without much effect ; five or six hours after 

 the first dose, twenty minims more were administered, which, 

 in half an hour, produced nausea and sickness, and in the 

 space of a few hours twelve copious and watery evacuations. 

 The secretion of urine was considerably increased. The other 

 case was that of a strong young man, also labouring under 

 dropsy ; twenty minims of the tincture were given, which pro- 

 duced nausea and copious watery evacuations. The next day, 

 ten minims more were given, with nearly the same results ; and 

 on the third day the purging had not entirely ceased. The 

 secretion of urine did not appear to be increased. The quan- 

 tity of resin administered to each patient was less than a 

 quarter of a grain. Dr. Paris, in the second volume of his 

 ' Pharmacologia,' gives an analysis of elaterium, and describes 

 the green resin as the active principle, to which he gives the 

 name of 'elatine' ; but the crystalline body appears to have 

 escaped his observation entirely, probably from his having 

 operated on very small quantities. 



CONTRIBUTIONS TO THE PHYSIOLOGY OF VISION. 



No. II. 



On the Insensibility of the Retina to feebly -illuminated Ob- 

 jects, when continuously presented. In accounting for the 

 beautiful and extraordinary phenomenon described at page 111 

 of this volume, I have admitted as an established fact, that 

 weak impressions on the retina become obliterated when ren- 

 dered continuous. To confirm the explanation there offered, 

 it will be satisfactory to adduce a few instances equally illus- 

 trative of the rule, which is only one case of a more general 

 law, confirmed by numerous observations, viz., that all luminous 

 objects, when continuously presented to the same points of the 

 retina, become invisible ; and that the rapidity of their dis- 

 appearance is in proportion to the feebleness of the light emitted 

 by or reflected from the object. Astronomers are well aware 

 that, on looking intently at a star through a telescope, it will 

 sometimes completely disappear, and again become visible on 



