MICRO-ORGANISMS AND DISEASE, 



INTRODUCTION. 



THE relation of micro-organisms to the infectious diseases 

 is admitted to be very intimate ; and although it may not be 

 quite so universal as some are inclined to assume, it is never- 

 theless definitely proved to exist as regards some of the 

 infectious maladies affecting man and brutes. In order to 

 pass in review all the ascertained facts and observations in 

 this vast and constantly-growing field of pathology, and to 

 appreciate and to assign their true value to the many 

 observations bearing on this relation of micro-organisms to 

 disease, it is necessary that the reader, and still more the 

 worker in this field, should be enabled to criticise the ob- 

 servations and facts brought forward by the numerous 

 writers on the subject, for otherwise he would probably take 

 as proved what has really not passed beyond the stage of 

 possibility. And it is this point which requires the most 

 careful attention, viz., to be able to see at a glance that, 

 owing to the imperfect or faulty method of investigation 

 employed, or that, owing to certain inferences incompatible 

 with the general laws and general tendency of the well- 





