BACTERIOLOGICAL INTRODUCTION 



THE theory that infectious diseases were due to 

 the presence of living organisms and that the 

 characters of such diseases could be referred to the 

 nature of the "contagium vivum" is of considerable 

 antiquity. It is only of recent years, however, that 

 proof of this position has been obtained, and that a 

 large number of infections in man and the lower 

 animals have been traced to the action of parasitic 

 micro-organisms which have gained access to the 

 tissues. These micro-organisms are for the most 

 part unicellular plants belonging to the lowest 

 division of the vegetable kingdom. They are 

 grouped under the name of Schizomycetes, or " fission 

 fungi," as a sub-division of the Fungi ; or, perhaps 

 better, as Schizophytes (F. Cohn), and regarded as 

 closely related to the Algse. 



Organisms belonging to other allied groups e.g., 

 the Hyphomycetes and Blastomycetes are known to 

 produce diseases of animals and plants, but nearly 



