Licence: In copyright
Credit: Alcoholic fermentation / by Arthur Harden. Source: Wellcome Collection.
![regarded as a living organism probably belonging to the vegetable kingdom. Alcoholic fermentation was observed to depend on the presence of living yeast cells, and was attributed to some effect of their vegetative life (quelque effet de leur v^gdtation). It was also noticed that yeast was not deprived of its fermenting power by exposure to the temperature of solid carbonic acid, a sample of which was supplied to Cagniard-Latour by Thilorier, who had only recently prepared it for the first time. Theodor Schwann [1837, 239], whose researches were quite inde- pendent of those of Cagniard-Latour, approached the problem from an entirely different point of view. During the year 1836 Franz Schulze [1836, 238] published a research on the subject of spontaneous gener- ation, in which he proved that when a solution containing animal or vegetable matter was boiled, no putrefaction set in provided that all air which was allowed to have access to the liquid was previously passed through strong sulphuric acid. Schwann performed a very similar experiment by which he showed that this same result, the absence of putrefaction, was attained by heating all air which came into contact with the boiled liquid. Wishing to show that other processes in which air took part were not affected by the air being heated, he made experiments with fermenting liquids and found, contrary to his expectation, that a liquid capable of undergoing vinous fermentation and containing yeast did not undergo this change after it had been boiled, provided that, as in the case of his previous experiments, only air which had been heated was allowed to come into contact with it. Schwann’s experiments on the prevention of putrefaction were un- exceptionable and quite decisive. The analogous experiments dealing with alcoholic fermentation were not quite so satisfactory. Yeast was added to a solution of cane sugar, the flask containing the mixture placed in boiling water for ten minutes, and then inverted over mer- cury. About one-third of the liquid was then displaced by air and the flasks corked and kept inverted at air temperature. In two flasks the air introduced was ordinary atmospheric air, and in these flasks fermen- tation set in after about four to six weeks. Into the other two flasks air which had been heated was led, and in these no fermentation occurred. As described, the experiment is quite satisfactory, but Schwann found on repetition that the results were irregular. Some- times all the flasks showed fermentation, sometimes none of them. This was correctly ascribed to the experimental difficulties, but none the less served as a point of attack for hostile and damaging criticism at the hands of Berzelius (p. 7).](https://iiif.wellcomecollection.org/image/b28108450_0022.jp2/full/800%2C/0/default.jpg)
