vi PREFACE 



has been thought desirable. The author wishes to express his 

 indebtedness to the council of the Ophthalmological Society 

 for its permission to reproduce some of the illustrations, 

 and to his friend Dr. William Campbell Posey, at whose 

 instigation and with whose kindly aid the lecture has been 

 reproduced in its present form. E. T. C. 



LONDON, 1922 



