INTRODUCTION 5 



and many modern systematists are inclined to return to his work 

 to establish authoritative terminology for present use. He re- 

 garded the bacteria as animals. Ferdinand Cohn (1872) recog- 

 nized the nature of bacterial spores, showed the close relation- 

 ship of bacteria to the algae and established their classification 

 in the plant kingdom. He distinguished six genera micro- 

 coccus, bacterium, bacillus, vibrio, spirillum and spirochaeta. 

 Migula (1897) undertook an extensive revision of bacteriological 

 nomenclature and classification, basing it upon morphological 

 characters, and his system is doubtless the most satisfactory yet 

 offered. The subject is still in a very unsettled state, neverthe- 

 less, and there is no system of classification generally accepted 

 by bacteriologists. The problem presents so many difficulties 

 and our knowledge of the bacteria is still so incomplete that many 

 authorities seem prone to consign systematic classification to the 

 future, and to employ names of sufficient historical prominence 

 to insure their correct interpretation. 



Fermentation and Putrefaction. The relation of micro- 

 organisms to the decomposition of organic matter, fermentation 

 and putrefaction, was one of the first fields of applied bacteri- 

 ology to be studied. Following the observation of bacteria in 

 saliva by van Leeuwenhoek in 1683, micro-organisms were dis- 

 covered in all sorts of decomposing material. At first, these or- 

 ganisms were regarded as unimportant for the chemical process 

 and interest attached chiefly to the question of their origin, 

 whether by spontaneous generation or from previously living 

 cells. Needham (1745) directing his attention more particularly 

 to this first question, boiled an infusion of meat, and keeping it free 

 from contact with the air, nevertheless observed after some days 

 the presence of "infusoria." Spallanzani (1765) repeated Need- 

 ham's experiments, subjecting hermetically sealed flasks of meat 

 infusion to the temperature of boiling water for one hour, 

 and he found no subsequent development of life and no decom- 

 position of the infusion as long as it remained sealed. While 

 discussion continued concerning the discrepancy between the 



