6 BACTERIA AND SOIL FERTILITY 



generation of these forms of life. This objection was answered 

 by the work of many an ingenious investigator. Schulze, in 1836, 

 passed air through strong acids and then into boiled infusions and 

 failed to find any living organisms in the infusion, whereas 

 Schwann passed the air through highly heated tubes with the same 

 results. This was criticized by their opponents who claimed that 

 the chemical alteration of the air subjected to such drastic 

 treatment had been responsible for the absence of bacteria in the 

 infusion. The work of Schroeder and Dusch (1853) ^^^ more 

 convincing, for they found that it was sufficient to stopper the 

 bottles with cotton plugs 5 the air passed in, but the microorganisms 

 were held back by the cotton and the contents of the flasks kept. 



Every now and then the contents of a flask would spoil, even 

 after it had been carefully stoppered and boiled. This remained 

 a stumbling block in the way of those who maintained that life 

 sprang only from life, until in the year 1865 when Pasteur dem- 

 onstrated that many bacteria may pass into a resting stage, and 

 while in this condition they will withstand conditions which 

 quickly kill them while in the vegetative stage. Eleven years 

 later Conn of Breslau investigated very carefully organisms in 

 this resting or spore stage, and today we know forms of microor- 

 ganisms which will withstand boiling water for sixteen hours 

 without being killed, and others even resistant enough to endure 

 for many hours a 10 per cent solution of carbolic acid. 



Since the dawn of history man has been interested in the won- 

 derful process known as fermentation, but although many an in- 

 genious theory has been formulated to explain it little more than 

 theory existed until the classic works of Pasteur on fermentation 

 appeared about 1837. Pasteur claimed that all forms of fermen- 

 tation were due to the action of microscopic organized cells. An 

 idea such as this, even at this late date, did not go unchallenged; 

 for we find no less illustrious workers than Helmholtz and Liebig 

 opposing it. The latter even scoffed at such an idea, writing: 

 "Those who pretend to explain the putrefaction of animal sub- 

 stance by the presence of microorganisms reason very much like 

 a child who would explain the rapidity of the Rhine by attributing 



