Thenard's memoir was followed by a communication of fundamental importance from Gay-Lussac [1810]. A process for preserving food had been introduced by Appert, which consisted in placing the material in bottles, closing these very carefully and exposing them to the temperature of boiling water for some time. Gay-Lussac was struck by the fact that when such a bottle was opened fermentation or putrefaction set in rapidly. Analysis of the air left in such a sealed bottle showed that all the oxygen had been absorbed, and these facts led to the view that fermentation was set up by the action of oxygen on the fermentable material. Experiment appeared to confirm this in the most striking way. A bottle of preserved grape-juice was opened over mercury and part of its contents passed through the mercury into a bell-jar containing air, the remainder into a similar vessel free from air. In the presence of air fermentation set in at once, in the absence of air no fermentation whatever occurred. This connection between fermentation and the presence of air was established by numerous experiments and appeared incontestable. Fermentation, it was found, could be checked by boiling even after the addition of oxygen, and hence food could be preserved in free contact with the air, provided only that it was raised to the temperature of boiling water at short intervals of time. Gay-Lussac's opinion was that the ferment was formed by the action of the oxygen on the [p005] liquid, and that the product of this action was altered by heat and rendered incapable of producing fermentation, as was also brewer's yeast, which, however, he regarded, on account of its insolubility, as different from the soluble ferment which initiated the change in the limpid grape-juice. Colin, on the other hand [1825], recognised that alcoholic fermentation by whatever substance it was started, resulted in the formation of an insoluble deposit more active than the original substance, and he suggested that this deposit might possibly in every case be of the same nature.