782 DR FRASER ON THE PHYSIOLOGICAL ACTION 



tigma-myosis may exist in one eye, while atropia-mydriasis is present in the 

 other. It is easy to prove the presence of the extract within the eyeball, after 

 its topical application, by removing the aqueous humour and placing it on the 

 conjunctiva of another animal, when the usual effects of Calabar bean on the pupil 

 will be produced. 



In addition to this phenomenon, increased lachrymation, and congestion of 

 the conjunctiva, and, I believe, of the iris itself, are produced. 



The question of the effects produced on the eye by the topical application of 

 such substances as physostigma and atropia must always be an interesting 

 one to physiologists. Its full discussion would require a special paper, so 

 numerous are the data to be considered, and so conflicting the opinions that have 

 been expressed. Besides, there are some effects that can only be conveniently 

 examined in man, and which must be included in any satisfactory review of this 

 attractive subject. It is, however, quite within the purpose of the present inves- 

 tigation to consider the method in which the iris is expanded by physostigma. 

 I have already expressed an opinion that iridal changes appear to require the 

 co-operation of special radiating and circular muscular fibres, with a system of 

 contractile blood-vessels possessing to a certain extent the properties of erectile 

 tissue. A mere antagonism between the two former muscular arrangements 

 could not alone account for the effects of either physostigma or atropia; and, 

 indeed, the actions of those substances seem to oppose such a theory. All 

 the muscular fibres in the iris are unstriped, and physostigma relaxes while 

 atropia contracts sucfi fibres. Therefore, were these the only causes of iridal 

 movement, physostigma would produce no effect on the pupil; for it would 

 merely render less energetic the contraction of both, and would not thereby 

 disturb their counterbalancing antagonism. For a similar reason, atropia will 

 merely increase the opposing action of both, without causing any iridal 

 movement. 



To reconcile their actions with this anatomical arrangement, it is necessary to 

 make one of the following very improbable suppositions — that the circular 

 muscle at the pupillary margin has different physiological properties from the 

 dilator ; or that the one set of fibres is regulated by nervous ganglia that can 

 be stimulated by the contact of substances, which paralyse corresponding ganglia 

 whose power is limited to the other set. 



Let it be granted, however, that dilator and constrictor muscles with counter- 

 balancing powers exist, and that, in addition, a system of contractile blood- 

 vessels is present, and the ascertained physiological actions of these opposing 

 substances will be rendered available for the explanation of their peculiar effects. 

 Dilatation of the pupil by atropia will then be due to the successful opposition of 

 radiating muscular fibres and contractile iridal blood-vessels, to unaided con- 

 strictor fibres ; the contact of atropia causing contraction of all unstriped fibres, 



