vi PREFACE. 



I am publishing these lectures with a feeling 

 of sincere gratitude for the kind and hospitable 

 reception which I received in London from my 

 friends and colleagues, and especially am I 

 anxious to express my indebtedness to Professor 

 William R. Smith for all his kindness, which 

 rendered my visit so enjoyable. I would also 

 desire to thank Dr. Carl Prausnitz for his very 

 valuable help, and Professor R. Tanner Hewlett 

 for kindly revising the English translation of 

 the Lectures. 



P. EHRLICH. 



FRANKFORT, 



April 22, 1908. 



