vi PREFACE TO THE SECOND EDITION 



tion of the Eye ; 5 and 12 from Crocker and Matthew's Theoretical 

 and Experimental Physical Chemistry. To all these authors and 

 to their publishers, Messrs. J. and A. Churchill, I desire to express 

 my thanks. 



I am indebted to Messrs. Baird and Tatlock, London, for the 

 loan of the blocks for Figs. 8, 18, 22, 45, 53, 67, 104, 106 and 109. 



I wish to record my thanks to Miss E. M. Paul, of the King 

 Edward School of Art, Armstrong College, for the original drawing 

 for Fig. QQ, and to Mr. J. Robson for the rough drawings from 

 which all the other new illustrations were made. 



DAVID BURNS. 



University of Durham College of Medicine, 

 Newcastle-upon-Tyne. 



