DEVELOPMENT OF SOIL BACTERIOLOGY 7 



it to the violent motions imparted to it in the direction of Burgen 

 by the numerous wheels of the mills of Venice". However, 

 Pasteur's carefully planned experiments soon demonstrated that 

 without microorganisms there would be no fermentation, no pu- 

 trefaction, no decay of any kind except by the slow process of 

 oxidation. 



If there were any doubts left in the minds of the scientific 

 world as to the fallacy of the theory of spontaneous generation, 

 after the work of Pasteur, they were dispelled by the work of 

 Tyndall. Tyndall proved that in an atmosphere devoid of dust, 

 as on the tops of mountains and in some ingeniously constructed 

 boxes used by him, perishable substances, such as beef tea, if 

 sterile, when placed in such an atmosphere, will keep for an 

 indefinite period. 



We have found the two great landmarks in the history of 

 bacteriology to be the discovery of bacteria by Leeuwenhoek and 

 the recognition by Pasteur that putrefaction, fermentation, and 

 decay are due to microorganisms which have parents as do other 

 plants or animals. A third great advancement was made in 1876 

 when Weigert used some of the anilin dyes to stain the body of 

 bacteria, thus making it possible to see and study the shape and 

 structure of organisms which may occur in body tissue, soils, milk, 

 and water. Still a fourth milestone on the path of bacteriological 

 research was passed when the immortal Robert Koch devised the 

 gelatin-plate method for obtaining pure cultures of bacteria. He 

 added to liquefied portions of sterile gelatin small quantities of 

 the material containing the bacteria which he wished to study, 

 shook the material to distribute it uniformly throughout the liquid 

 gelatin and spread it on a covered sterile plate. The bacteria were 

 fixed in isolated spots. The bacteria multiplied until they became 

 visible to the naked eye, just as a clump of trees in the valley may 

 be seen while a single tree may be invisible from the distance. 

 These colonies, each the offspring of a single cell, could furnish 

 only one kind of bacteria. These could be fished out with a sterile 

 platinum needle, studied under the microscope or grown in differ- 

 ent media, or perchance in soil or the body of susceptible animals 



