P E E F A C E 



In the following pages ai'e set forth the results of a long and conscientious 

 experimental study of the venom of the Rattlesnake. 



During a large part of two years I have given to this work almost all the leisure 

 which could be spared from the everyday exactions of my regular professional 

 duties. 



In its progress, I have been constantly aided and encouraged by many friends, 

 principally members of the Academy of Natural Sciences, of Philadelphia; more 

 especially am I in debt to my fellow-members of the Biological Department of the 

 Academy, to Prof Wm. A. Hammond, and to Mr. Vaux. 



My thanks are due to the Smithsonian Institution, without the aid of which 

 I should have been unable to procure the serpents which were essential to my 

 purposes. 



The historical references and the Bibliography owe much to the manuscript notes 

 of Prof John Le Conte, which were collected with much care and labor, that they 

 might be used in a research which he at one time contemplated. Becoming aware 

 of the investigation in which I was engaged, he most liberally placed at my dis- 

 posal this collection of literary materials. 



To Drs. Brinton and Kane I am greatly obliged for intelligent assistance in 

 numerous experimental investigations, for which their ready surgical skill so well 

 fitted them, and I am also in debt to Messrs. Cantrell and Picot, for like aid, which, 

 owing to the nature of the service, was not always free from danger. My thanks 

 are further due to Drs. La Roche and Stille, to Dr. Fisher, the librarian of the 

 Academy of Natural Sciences, and to Dr. T. H. Bache, the librarian of the College 

 of Physicians, whose assistance in consulting its extensive collection of American 

 journals has been to me of great service. 



With the exception of the microscopic delineations, the plates were drawn by 

 Dr. Packard, from my recent dissections, and owe their chief merit to his accurate 

 pencil. 



The conclusions arrived at in the pages of this Essay, rest alone upon experi- 



