THEORIES OF FERMENTATION. 231 



fermentation, a view confirmed by the practical experience 

 that sulphurous acid could be used for fuming out casks to 

 arrest the fermentation of must, because the conversion of 

 sulphurous acid into sulphuric acid brought about the removal 

 of oxygen from the air of the casks. 



The importance of yeast for the fermentation process was 

 quite overlooked. It was regarded as a precipitation from 

 the liquid of no further importance for the comprehension of 

 the process. The first indication of the true relationship had, 

 however, been discovered at a much earlier period. 



About the year 1600 two Dutchmen, Hans and Zacharias 

 Janssen, invented the microscope, and in the latter half of 

 the seventeenth century another Dutchman, Leeuwenhoek, 

 issued his renowned letters on the investigation of different 

 substances undertaken with the help of this instrument for 

 the Royal Society. In 1680, in the course of one of his letters, 

 a description and drawing of beer yeast appeared for the first 

 time, and later in the same year one of wine yeast. Shortly 

 after the first clear sketches of bacteria appeared. He held 

 the view that the globular yeasts were derived from the flour 

 of cereals used in brewing, and he compared them with starch 

 granules. He had, however, no glimmering of the importance 

 of yeast for fermentation. 



The observations of the learned Dutchman regarding the 

 microscopical " animals/' for so he named the bacteria, origin- 

 ated the great discussion which has extended into our time, 

 involving researches and explanations of the important question 

 as to whether these organisms can be derived from inorganic 

 and dead matter, or whether they are derived from external 

 fermenting and living matter. The whole of the following 

 development is based upon the investigation of this question, 

 ' which naturally had its influence in the domain of fermentation. 



After the fairy tales of earlier times had been disproved, 

 Needham came forward in 1745 with definite experiments 

 designed to show that the lowest microscopical forms of life, 

 the " infusoria," were created in the following way : He 

 exposed decoctions of meat and other organic substances to 

 such a high temperature that, according to his views, all 

 forms of living matter must be killed, and the vessels were 



