1885.] produced by the Application of Cocaine to the Eye. 441 



also weak is shown by the ease with which myotics (Experiment IV 

 and V) and stimulation of the 3rd nerve (Experiment VIII) overcome 

 the mydriasis. , 



Therefore our facts bring ns to the conclusion that cocaine mydri- 

 asis is induced by a local irritation of the endings of the cervical 

 sympathetic or mydriatic nerve in the eye. But this nerve consists of 

 two distinct sets of fibres — one set acting on the blood-vessels as a 

 vaso-constrictor, and the other only producing dilatation of the pupil. 

 That such is the case can be proved by bleeding an animal to death 

 w r hen, even after several excitations of the cervical sympathetic, fresh 

 stimulation of this nerve again increases the dilatation of the pupil 

 induced by the bloodless state of the eye. Francois Franck, in his 

 able monograph " On the Dilatator Nerves of the Pupil," * brings 

 forward several other conclusive arguments to prove the dual action 

 of the cervical sympathetic fibres. That cocaine acts on the small 

 blood-vessels by constricting them can be proved easily by its action 

 on the vessels of the conjunctiva. 



We may therefore assume that it also acts thus on the vessels of 

 the iris — a fact which accounts for the diminution of tension in an eye 

 under cocaine. But that this is not the only cause of cocaine mydri- 

 asis is evident from the following facts, viz., that the full mydriasis 

 of cocaine is much larger than that induced by the bloodless state of 

 the eye, and that cocaine increases the mydriasis induced by bleeding 

 the animal to death (Experiments XI and XIII). It is the action on 

 the purely mydriatic fibres that gives rise for a time to dilatation of 

 the pupil by cocaine after section of the cervical sympathetic (Ex- 

 periment XV). That this action of cocaine on the purely mydriatic 

 fibres passes off after a time is shown on rabbits by Experiment XVII, 

 and this is due to cutting off its communication with the mydriatic 

 centre of Budge and Waller in the spinal cord. 



The reason of this happening so soon is the weak stimulus due to 

 cocaine, and therefore a very slight change in the nerve endings being 

 able to prevent its action. That cocaine also acts on this mydriatic 

 nerve is suggested by the enlargement of the palpebral aperture fol- 

 lowing its application. Hence from these experiments it appears that 

 cocaine produces mydriasis by acting locally on the endings of the 

 cervical sympathetic nerve in the eye, and also that it affects both sets 

 of fibres, namely, the purely mydriatic and the vaso-constrictor. 



* " Travaux du Laboratoire de Marey," Annees IS77-79. 



