42 SILOS, ENSILAGE AND SILAGE. 



were living organisms that derived their nourishment 

 from sugar and thus produced the phenomena of fer- 

 mentation. This was in effect the first announcement 

 of the true theory of fermentation, but from the prom- 

 inence given to the popular chemical hypothesis, it was 

 soon overlooked and forgotten. 



In 1838 Cagniard de la Tour (who was afterwards 

 elected to succeed Gay-Lussac in the Paris Academy of 

 sciences) re-discovered the yeast granules of Leuwen- 

 hoek, and found them to be minute plants that were 

 multiplied by a process of budding, and these he claimed, 

 in the processes of their nutrition, were the cause of fer- 

 mentation, as had been asserted by Astier twenty-five 

 years before. " The chemists, with Berzelius and Liebig 

 at their head, at first lauged this idea to scorn,"* but 

 Schultze and Schwann, about the same time (1836-8), 

 by the simple device of passing air through red-hot 

 tubes, or through sulphuric acid, to destroy any organic 

 germs associated with it, without altering its proportion 

 of oxygen, proved that it did not excite fermentation 

 when introduced into infusions of fermentable materials 

 that had previously been boiled, which was of course 

 fatal to that part of the chemical theory of fermentation 

 which made oxygen an active agent in the process. 



Helmholtz, in 1843, was equally successful in demon- 

 strating the fact that the liquids or the gases of ferment- 

 ing materials had no power to excite fermentation. He 

 separated putrescent and fermenting liquids from putres- 

 cible and fermentable materials b} a simple membrane 

 which allowed the fluids and gases to pass through it by 

 osmosis, but did not permit the transfer of the solid par- 

 ticles from one side to the other. As the process of fer- 

 mentation or putrefaction, under these conditions, was 

 confined to one side of the membrane, it is evident that 

 the cause of fermentation was something that could not 



* Huxley, British Association Address, 1870, Nature, 11, 402. 



