OPENING ADDRESS. 17 



logical facts which seemed to indicate, that the pupil 

 might be made to expand even when this sphincter was 

 not affected. Some physiologists therefore demanded a 

 second radial muscle, which by its contraction could pull 

 out the pupil — a so-called dilator muscle with radial fibres 

 like spokes in a wheel. Although such fibres exist in the 

 birds eye, none were found in the mammalian iris, and it 

 was therefore thought to be vain to assert from experiment 

 their presence. The observed phenomena must, it was 

 said, be capable of some other interpretation, active 

 expansion was thought to be impossible. In 1892, a 

 discovery made simultaneously and independently by Lang- 

 ley* and Heesef showed definitely that in the cat the 

 iris could be made to expand actively. If its edge be 

 stimulated by suitable electric currents led through the 

 corneo-sclerotic junction the pupil is not constricted but 

 expands at that point and by shifting the site of the stim- 

 ulation this local expansion is similarly shifted. Careful 

 examination of the iris shows that two movements occur 

 in it, each confined to the neighbourhood of the stimulated 

 part. Immediately the stimulation begins there occurs a 

 localised puckering of the pupil all radial lines at this 

 point being brought visibly nearer one another; this must 

 be due to the contraction of the circular sphincter. As 

 the stimulus is kept on, there is suddenly seen a new 

 puckering causing folds which are piled up near the edge 

 and are circumferential, whilst the pupil at this point 

 expands. The two movements are now seen to be going on 

 in the iris at the same time. After the stimulation has 

 ceased, the sphincter puckering, which was the first to begin 

 stops, and now the second series of folds is seen by itself. 

 This is a demonstration ad oculos and in oculo, that there 



* Langley and Anderson. Journal of Physiology, Vol. XIII, p. 555. 

 t Hr.ese. Pfliigers Archiv. Vol. LII, p. 535. 



