10 AGRICULTURAL BACTERIOLOGY 



in sour milk a trace of grayish substance, and had proved it 

 to be a ferment of milk. He had before him one of the 

 most important of the bacteria. This work was the begin- 

 ning of the new science of bacteriology. 



Pasteur accepted the challenge of the Paris Academy, 

 and on April 7, 1864, he gave his results to the world in a 

 famous lecture at the Sorbonne. He showed that if any 

 solution containing organic matter is heated long enough, 

 and protected from the microorganisms in the air, it will 

 remain unaltered. He avoided the objections that had been 

 urged against the experiments of others by allowing air to 

 pass in and out of his flasks through long curved tubes, on 

 the walls of which all dust and bacteria would be deposited. 

 He showed for all time that life comes from life, that every 

 form is the progeny of preexisting forms of like nature. 



The importance of this work of Pasteur can not be over- 

 estimated, for it led him to continue the study of microor- 

 ganisms until his death, in 1895. Pasteur's influence on the 

 material side of human life has probably been greater than 

 that of any other man. 



Aniline dyes. The discovery of the bacteria by Leeu- 

 wenhoek, and the recognition of their relation to decompo- 

 sition by Pasteur, are two great landmarks in the history of 

 bacteriology. Another was the accidental discovery of the 

 aniline dyes by Perkin in 1856. The recognition of the bac- 

 teria, as they occur in many places, especially in the fluids 

 and tissues of the animal body, is impossible unless they 

 can be differentiated by stains from the other materials. 

 The aniline dyes were first used for the staining of bacteria 

 by Weigert in 1876. 



Another great advance in the progress of the science was 

 the development by Robert Koch, a German physician, of 

 a method of separating one kind of bacteria from other 

 kinds with which it might occur. His work enables the 



