Vlil PREFACE. 



let the world know with what results my labors 

 have been rewarded, and with the hope that it 

 may be the means of inducing others to pursue 

 like investigations. 



In prosecuting my studies, I have had no prec- 

 edents to guide me, no literature to consult, 

 and no land-marks by which to steer my course. 

 I have, therefore, been compelled to find my own 

 means, suggest my own experiments, and solve 

 my own problems. Not a line on this subject is 

 to be found in all the literature of the world ; and 

 yet the results which I have obtained have far 

 surpassed my highest hopes. Considering the 

 difficulties under which I have been compelled 

 to work, I have been rewarded with results for 

 which I dared not hope, and this inspires me to 

 believe that my success will meet my highest 

 wishes when I am placed in touch with such 

 subjects as I expect to find in the forests of trop- 

 ical Africa. 



The records in Part I. of this volume are only 

 a few of my experiments ; but as they illustrate my 

 methods and set forth the results, they will serve 

 to show, in a measure, the scope of my work. 

 I shall not describe like experiments only in 

 so far as may be found proper to confirm the de- 



