PREFACE. 



The main objects of the publication of this sketch, 

 which in part originally appeared in separate papers, 

 are to assist future investigators in discovering what 

 has already been done to throw light upon the 

 difficult subject of which it treats, so that their time 

 may not be wasted in useless investigations • and to 

 prevent an unnecessary and reckless sacrifice of 

 auimal life. Experiments performed upon the lower 

 animals, either in ignorance of what has already beeD 

 accomplished, or out of mere scientific curiosity, are 

 alike inexcusable. But, unfortunately, owing to the 

 want of some such little work as this, investigators 

 have sometimes unconsciously travelled over the 

 same grouud, only to prove that which had already 

 been placed beyond doubt. An old friend once 

 remarked to the author that he thought the conduct 

 of these researches was a useless expenditure of 

 time and labour, for, said he, " Contra vim motris non 

 herbuld crescit in hortis." But if we are to interpret 

 this old saw as meaning that all scientific enquiries 

 directed towards the prevention of death are worth- 



