INTRODUCTION AND DEDICATION. 



TO THE CANDIDATES FOR GRADUATION IN THE JEFFERSON 

 MEDICAL COLLEGE, OF THE SESSION OF 1846-1847: 



GENTLEMEN : 



To you, I had the honor of delivering, nearly in their 

 present shape, the lectures which I now send to the press. 

 Previously, I had not put my ideas on the subject of which 

 they treat, into so formal a shape, although I had an- 

 nounced for years, to each successive class, my impression, 

 that possibly, the protophytes might afford a good expla- 

 nation of the causation of malarious, and other diseases 

 of a febrile nature. Of the production thus, at least of 

 yellow fever and cholera, I entertained less doubt, and 

 taught, therefore, the sentiment with less reserve. But, 

 although urged by some of you, and more formally re- 

 quested by the class by which you were immediately suc- 

 ceeded, to place my opinions on this subject before the 

 public, I refrained from their publication through aversion 

 to controversy, and the hope that time would bring more 

 conclusive evidence of their truth or falsehood. Other 

 friends, whose age, position, and learning, entitled their 

 opinions to the highest respect, did me the honor to listen 

 to my elucidations, and to recommend their publication. 

 Indeed, one of them, well known to you for his great 

 learning and refined eloquence, wrote to Dr. Forbes, of 



