6 MICRO-ORGANISMS AND DISEASE [intro. 



cutaneously or intraperitoneally, is not of a specific nature 

 and is not of the nature of typhoid fever in man. As a 

 last example we may mention leprosy. No one doubts that 

 the bacilli so peculiar in their morphological and biological 

 characters and in their distribution, which are found 

 crowding the cells and tissues of the leprosy nodules, 

 are the real microbe of leprosy, but no one has succeeded 

 as yet in producing leprosy in an animal. 



It will be my aim in the following pages, first to describe 

 the methods that may be employed with success in inves- 

 tigations bearing on the relation of micro-organisms to 

 disease ; secondly, to describe in conformity with reliable 

 observations the morphology and physiology of the micro- 

 organisms that bear any relation to disease ; and thirdly, to 

 enumerate the principal observations that have been made 

 in recent years to prove the existence of such an intimate 

 relation. Last, but not least, we shall consider the precise 

 relation of the principal micro-organisms and their chemical 

 products to the causation of disea'se. 



