436 



Mr. W. H. Jessop. On the Mydriasis [June 18, 



Right pupil, 6 mm., does not act to light or accommodation. 



Cocaine, 2 per cent., twice applied, and pupil 9'5 mm. 



Black and White E-abbit. — Pupils 5*5 mm. X 6*5 mm., and act well. 

 Skull cap removed, and 3rd nerves exposed. Right 3rd nerve cut ; 

 pupil = 6'5 mm. X 7*5 mm. ; nerve then irritated by faradaic current, 

 and pupil 3 mm. X 2 mm. Cocaine 2 per cent, twice put on right 

 conjunctiva, and pupil dilated soon to 8*5 mm. X 7 mm., and then to 

 10 mm. 



A weak stimulation of the 3rd nerve overcame the mydriasis, pro- 

 ducing the same myosis as before whilst the stimulant lasted, and 

 giving rise again to mydriasis. 



Experiment IX. 



On tapping the anterior chamber of an eye under the influence of 

 cocaine, the dilated pupil contracts very little or not at all. This is, 

 of course, contrary to what occurs in a normal eye, or in one under 

 atropine, where marked contraction of the pupil occurs in all cases. 



Experiment X. 



On tapping the anterior chamber of a rabbit, and placing one 

 electrode on the surface of the iris towards the centre, a weak faradaic 

 current gave rise to contraction of the pupil in all cases of cocaine 

 mydriasis, except two, in which very large mydriasis had been 

 produced. 



These latter, however, could be explained by the great stretching 

 of the sphincter muscle, and hence stimulation directly of the fibres 

 had no effect. 



Experiment XL 



On the detruncated head of a frog the application of cocaine to the 

 conjunctiva I have generally seen followed by mydriasis, a fact also 

 seen independently by Dr. Waller, to whom I must express my thanks 

 for numerous suggestions, and much help in my experiments. In my 

 first case and two others I failed to get any effect on the pupil. 



Experiment XII. 



On the exsected eye of rabbits I have tried several times, with 

 failure, to increase the size of the pupil by cocaine. In two cases, on 

 injecting cocaine into the anterior chamber immediately after exsec- 

 tion, the contraction of the pupil due to tapping soon passed off, and 

 the pupil became slightly larger than before tapping. 



Experiment XIII. 



On the eyes of rabbits which have been bled to death, cocaine gives 

 rise to an increase in the mydriasis produced by the effect of the 

 haemorrhage. 



