PREFACE 



THE subject of this work was the theme of an inau- 

 gural address to the Microscopical Society of Liverpool, 

 delivered by me as President for the year 1874. My 

 attention had been directed to the subject for several 

 years, and materials accumulated for the treatment of 

 it far beyond what could be given in the compass of a 

 lecture. These materials have been, to some extent, 

 used in the Second Part, and the rest were intended 

 for the Third Part of " Life, and the Equivalence of 

 Force," a work in which I have endeavoured to bring 

 before the notice of biologists the remarkable anticipa- 

 tion of certain recent views on the nature of life and 

 other physiological questions, contained in the, partly 

 posthumous, works of Dr. John Fletcher, of which I 

 am the sole surviving editor. It has seemed, however, 

 better to publish what refers to this subject complete 

 in itself, leaving my hands free for other matters, 

 especially the stimuli : hence the present book. As 

 no claim to original discoveries is here put forward, 



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