SILOS, ENSILAGE AND SILAGE. 43 



pass through the membrane, and that the liquids and 

 gases were entirely inert. 



Another assumption of Liebig's theory was thus dis- 

 proved by direct experimental evidence, and in the con- 

 troversy which was carried on for many years, we find 

 repeatedly enacted what Prof. Huxley terms "the 

 great tragedy of science the slaying of a beautiful 

 hypothesis by an ugly fact." 



These experiments, which in themselves appear to be 

 a conclusive refutation of the chemical theory, were 

 fully corroborated by the investigations of Schroeder 

 and Dusch in 1854, which were conducted on an entirely 

 different plan. They found that liquids which were 

 particularly liable to take on putrefactive or fermenta- 

 tive changes, were preserved indefinitely (after boiling, 

 to destroy all contained germs), when freely exposed to 

 air that had been filtered through cotton wool. As no 

 change in the composition of the air could be produced 

 by this process of filtration, aside from the removal of 

 the solid particles floating in it, these last must contain 

 the efficient causes of fermentation and putrefaction. 



The chemists, however, continued to ignore this accu- 

 mulation of evidence, which was in direct conflict with 

 Liebig's theory, and it remained for Tyndall and Pasteur 

 to clear up all possible doubts, and establish the biolog- 

 ical theory of fermentation by a series of experiments 

 that are unsurpassed in the history of science, for the 

 accuracy and skill with which they were planned and 

 conducted to answer all objections that had been raised, 

 and avoid all possible elements of error. 



Instead of filtering air through cotton, as in the exper- 

 iments of Schroeder and Dusch, another method of puri- 

 fying it was adopted by Tyndall with quite as satisfac- 

 tory results. "A chamber, or case, was constructed 

 with a glass front, its top, bottom, back and sides being 

 of wood. At the back is a little door which opens and 



