( iv ) 



Collier, who has allowed me to copy one of his 

 portraits of Huxley. 



With a whole-hearted response, I say thanks to 

 Messrs. Waterlow and Sons Limited. Without their 

 cordial and energetic co-operation it would not have 

 been possible to produce the work in the manner in 

 which it has been, or in the short time, less than 

 three months, available for printing and making the 

 collotypes. All the collotypes and most of the illus- 

 trations in the text were done by them. A few of 

 the illustrations in the text were done by the Northern 

 Photo Engraving Company, of Manchester. 



Lastly, I have to thank Mr. Walter Whitehead 

 for his encouraging stimulation, put in the character- 

 istic but terse phrase, " Peg away." I have done so 

 during intervals snatched from the routine work of a 

 rather busy session, and endeavoured to give as the 

 result of his often repeated " minimum stimulus " the 

 maximum response. In any case, like the heart, the 

 response is the best that I am capable of, and my 

 only wish is that the perusal of this work will give 

 as much pleasure to the reader as its production has 

 given to the writer. 



WILLIAM STIRLING. 



Physiological Laboratory, 



Owens College, Manchester, 



yuly \oth, 1902. 



