PREFACE. 



IT was with very sincere pleasure that I 

 accepted the invitation of the Council of the 

 Royal Institute of Public Health with which 

 they honored me, to deliver the Harben Lec- 

 tures in 1907, for many relationships both of a 

 scientific and social character have always con- 

 tributed to render a visit to England one of 

 stimulus and recuperation. 



The subjects which I chose for my lectures 

 are closely related with those questions, with 

 the study of which I have been connected during 

 the past ten years, viz., the theories of Immunity 

 and Atrepsy, which latter is connected with my 

 researches on Cancer, and the theory of 

 Chemico-therapeutics which I have enunciated 

 in connection with my work on the Trypano- 

 somes. 



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