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 observations 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 re- 

 quires the most careful attention, viz., to be able to see at a 

 glance that, owing to the imperfect or faulty method of inves- 

 tigation employed, or that, owing to certain inferences incom- 

 patible with the general laws and general tendency of the 

 well-founded and experimentally proved facts, the statements 

 set forth in a particular observation or series of observations 

 are not to be accepted. 



In all investigations of the relation of micro-organisms to 

 disease it is necessary to bear in mind that, as Koch 1 has 

 pointed out, no observation can be said to be complete, or, one 

 should rather say, in no instance can it be said to have been 

 satisfactorily proved, that a particular infectious disease is due 



* Die Milzbrand-impfung, Cassel and Berlin, 18S3. 



a B 



