88 MUSGRAVE. 



ami the elements necessary for its beginning and propagation and the 

 influences which antagonize or favor it are only slightly studied. 



The whole question is of the most intense interest and of the greatest 

 practical importance and offers one of the most promising fields for 

 research to he found at the present time. It is not inconceivable that 

 the whole process of parasitism, even in its greatest selectiveness, as for 

 example of tetanus toxin for the nervous system or of certain trypanoso- 

 mata for cerebro-spinal fluid, is evolutionary and there is not lacking 

 evidence which may be -used in support of such a hypothesis with more 

 logic than has hitherto been given in attempted explanation of many 

 phenomena. 



The most promising field for laboratory research in the future will be 

 the study of cause and effect, in the complex relations in which they 

 onur in nature, of the interrelation and interaction of microorganisms 

 with each other and in their environment of complex symbiosis and the 

 ever-changing and multiple conditions found in hosts. Attention to 

 individual components of microorganisms and specific manifestation 

 of resistance by hosts without being accompanied by a balanced concep- 

 tion of the influence of complex environment upon the details, has un- 

 doubtedly led to the elaboration of a considerable superstructure which 

 is useless if not dangerous in the study of pathology. 



