30 HISTORICAL INTRODUCTION 



Pasteur's researches furnishing a scientific basis for many 

 processes of change in the soil. In 1873 Schlosing and 

 Miintz showed that nitrification must be due to the action 

 of microorganisms, though the discovery of the particular 

 ones remained for Winogradsky in 1889. Thus the belief 

 that fermentation and putrefaction are due to microorgan- 

 isms was as well established by the early eighties of the last 

 century as that similar organisms are the causes of infectious 

 diseases. 



STUDY OF FORMS. 



An important part of the scientific knowledge of living 

 organisms is dependent on a study of their forms and rela- 

 tionships. As has been stated, Leeuwenhoek considered 

 bacteria to be "animalcules" because they showed inde- 

 pendent movement. But little attention was paid to the 

 natural history of these animalcules for nearly a hundred 

 years after Leeuwenhoek. Dm-ing the last quarter of the 

 eighteenth century, however, workers busied themselves 

 chiefly with the discovery and description of new forms. 

 Among these students were Baron Gleichen, Jablot, Lesser, 

 Reaumur, Hill and others. IMiiller, of Copenhagen, in 1786 

 published the first attempt at classification, a most impor- 

 tant step in the study of these organisms. Miiller intro- 

 duced the terms Monas, Proteus and Vibrio which are 

 still in use. Ehrenberg, in his work on Infusoria, or the 

 organisms found in infusions, published in 1838, introduced 

 many generic names in use at present, but still classed the 

 bacteria with protozoa. Joseph Leidy, the American geol- 

 ogist, who took great interest in natural history in general, 

 considered that the "vibrios" of previous writers were plants 

 and not "animalcules." He seems to have been the first to 

 have made this distinction (1849). Perty (1852) recognized 

 the presence of spores in some of his organisms. Ferdinand 

 Cohn (1854) classed the bacteria among plants. Nageli (1857) 

 proposed the name " Schizomycetes" or "fission fungi," 

 which is still retained for the entire class of bacteria. Cohn 

 in the years 1872-1875 established classification on a mod- 

 ern basis and added greatly to the knowledge of morphology 



