440 



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



To make certain of this result, Mr. Nettleship and myself made ten 

 days afterwards the following observations on the patient : — - 



In a good light. 11.15. a.m. right pupil 2 mm., left 2'5 mm.; 1 disk 

 of cocaine grain placed in each eye. 



11.18, three more disks of same strength put in each eye. 



11.25, right pupil 2 mm., left 4 5 mm. 



11.35, right pupil 2 mm., left 6 5 mm. 



11.55, right pupil 2 mm., left 7 mm. 



12.10, pupils the same ; on shading them the right pupil 3 mm., 

 left 9 mm. 



On now putting homatropine into the right eye the pupil dilated 

 regularly as in a normal eye as below : — 



12.15 p.m., homatropine (4 grains to the ounce) put in right eye ; 

 pupil was 2 mm. 



12.30, right pupil now 6*5 mm., and does not act to light or accom- 

 modation. 



All the preceding experiments pointed to the action of cocaine being 

 an irritant of the sympathetic or mydriatic nerve of the eye, and this 

 fact is proved beyond a doubt by the last experiment (XVIII). Both 

 in rabbits in which a piece of the cervical sympathetic had been 

 excised for some days, and also in a case presenting all the symptoms 

 of section of the cervical sympathetic, cocaine had not the slightest 

 effect on the pupil. 



That such action is local and not central is proved by the extremely 

 local and limited action of cocaine on all the parts of the body, in- 

 cluding the pupil (Experiment I), and by dilatation of the pupil fol- 

 lowing its application to an exsected eye (Experiment XII). That 

 cocaine mydriasis is not in any way dependent on the 3rd nerve is 

 shown by Experiments VI, VII, and VIII, and also by the pupil 

 acting to light and accommodation (Experiment I). That cocaine 

 mydriasis is not due to paralysis of the sphincter muscle is shown by 

 the ease with which eserine, which acts directly on the muscular fibre, 

 reduces it, producing the usual myosis (Experiment IV), and also by 

 the fact that stimulation of the muscular fibre directly gives rise to 

 contraction of the pupil (Experiment X). 



The cases in which this contraction on direct stimulation did not 

 take place were due probably to the overstretching of the sphincter 

 muscle. Thus by excluding the other means of producing mydriasis 

 we have next to consider whether we can produce the same kind of 

 mydriasis as that of cocaine by excitation of the sympathetic. 



We find that the faradaic stimulation of the cervical sympathetic 

 which will give rise to a dilatation of the pupil, at the same time 

 acting to the reflex of light, is very weak, as any slight increase of 

 the current stops this reflex action of the pupil. But that the local 

 excitation of the sympathetic by cocaine and its induced mydriasis is 



