S3S 



inwards the pillars of the iris {g), so as to increase the con- 

 vexity of the cornea. Moreover, the fore part of the sclerotic 

 {q) would be also drawn inwards by means of those fibrous 

 bundles (r) which enter it at the posterior boundary of the 

 circular sinus {s). The effects of the changes here described 

 upon focal adaptation are too obvious to require further 

 elucidation. 



Experimenters have found — 1st. That the application of a 

 direct stimulant, viz. Calabar bean or galvanism, will pro- 

 duce contraction of the sphincter fibres of the iris and 

 thereby of the pupil. Sndly. That a sedative influence, such 

 as that of atropine, will induce relaxation of those fibres, and 

 consequent dilatation of the pupil. 3rdly. That alternate 

 stimulation of the third nerve and of the sympathetic respec- 

 tively will cause contraction and dilatation of the pupil. 

 4thly. That if the sympathetic twigs are paralysed, contraction 

 of the pupil will ensue, the j^assive antagonism, so to speak, 

 of the sphincter overcoming that of the radiating fibres ; 

 and conversely, that paralysis of the third nerve will give 

 rise to dilatation of the pupil, through relaxation of the 

 sphincter. 5thly. As instanced by Dr. D. Argyle Robertson,^ 

 that after the galvanic stimulus has ceased to produce con- 

 traction of the pupil in the recently dead iris, actual dilatation 

 takes place. Now, if it be admitted, as is most natural, that 

 stimulants or sedatives will induce contraction or relaxation, 

 as the case may be, in muscles sujoplied with nervous energy 

 from any source, whether it be cerebral, spinal, or sympa- 

 thetic, the following positions may be reasonably assumed to 

 account for all the foregoing phenomena : — 1st. That the 

 sphincter fibres are more powerful than the radiating. 2ndly, 

 That simple elastic force, supplementing the latter, would in 

 some measure make up the difference. 3rdly, That in all 

 probability agencies of a stimulating or depressing kind would 

 exert their influence, primarily on the cerebral nerves, and 

 secondarily upon the sympathetic, which is also known to 

 retain its irritability for a longer period (Budge). 4thly. 

 That, as in the normal play of the antagonistic radiating and 

 circular muscular fibres, when one set is in a state of con- 

 traction the other is relaxed, and vice versa, so, when 

 contraction or relaxation of one is induced by artificial 

 means, the opposite condition is likely to arise in the other as 

 an automatic consequence. The latter position is of great 

 importance, for by taking it into account the often contradic- 

 tory results of experiment may be reconciled. 



However necessary it may be to seek a physiological 

 1 'Lancet,' Feb. 5th, 1870, p. 212. 



