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 



