HISTORY OF BACTERIOLOGY 5 



ance and practice, that there is hardly anything else so diffi- 

 cult." Another worker who deserves special mention is Ehren- 

 berg (1795-1876). In 1836 he published his great work on 

 Infusoria, and in this treated of the bacteria as no one had be- 

 fore him. He recognized quite accurately the limitations of 

 this group and differentiated them from the true protozoa. He 

 also recognized the principal form types in which the bacteria 

 are usually divided. Another worker still should be men- 

 tioned, Ferdinand Cohn (1828-1898). He was Professor of 

 Botany in the University of Breslau. His works contributed 

 greatly to the advance of our knowledge of bacteria. A new 

 era in the history of bacteriology began with the work of 

 Louis Pasteur (1822-1895). Pasteur, although by inclina- 

 tion and training a chemist, was early led by his chemical 

 researches to the study of the relation of microorganisms 

 to various natural processes, such as fermentation, decay, 

 and putrefaction, and later to the relation of these organisms 

 to disease processes in man and animals. Later still he took 

 up the study of the scientific methods of preventing and curing 

 these diseases. Viewed from any stand-point, his researches 

 are of the profoundest importance. He introduced the 

 experimental method and used it with telling effect in the 

 study of bacteria and allied microorganisms. From an ob- 

 scure position, interesting only to the professional biologist, 

 Pasteur raised these microorganisms to a place of greatest 

 interest on account of their significance in the production of 

 changes of greatest importance to man. Pasteur may well 



