20 



DEVELOPMENT OF BACTERIOLOGY 



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many ingenious investigators. 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 criti- 

 cized by their opponents who claimed that the chemical alteration 



FIG. 2. Experiment of Schulze: Forcing air through sulphuric acid. (Lafar.) 



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) was more convincing, for they found that it was 

 sufficient to stopper the bottles with cotton plugs; the air passed 

 in but the microorganisms were held back by the cotton and the 



FIG. 3. Experiment of Schwann: Heating air to make it sterile. (Lafar.) 



contents of the flasks kept in good condition. 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 demonstrated that many bacteria may pass 



