10 MICRO-ORGANISMS AND FERMENTATION. 



liquids or other substances. SPALLANZANI warmed extract of 

 meat in closed flasks, and demonstrated that the contents 

 of the flasks remained unaltered until air is admitted. From 

 this he concluded that the germs which developed in the 

 opened flasks had come in from the air. Later (1*782) 

 SCHEELE demonstrated that vinegar may be prevented from 

 decomposing by the application of heat. But his discovery 

 was not heeded. In 1810 APPERT published his book on a 

 method of preserving various foods and liquids by means 

 of heat. In the fourth edition of his book, which appeared 

 in 1831, he gives directions for the treatment of wine, beer, 

 and other liquids, his method being essentially the same 

 as that employed to-day (the so-called " Pasteurisation "). 



To the following period, which was of such great import- 

 ance for micro-biology, belong the highly meritorious researches 

 of F. SCHULZE (1836) and TH. SCHWANN (1837), in which 

 it was shown that perishable liquids which had been vigorously 

 boiled in flasks would remain sterile if the air subsequently 

 admitted were made to pass through sulphuric acid or through 

 red-hot tubes. At the same time MITSCHERLICH, CAGNIARD- 

 LATOUR, SCHWANN, and KUETZING described the yeast cells, 

 KUETZING also describing the acetic acid bacteria. TURPIN 

 (1838) enunciated that most important doctrine: "No decom- 

 position of sugar, no fermentation without the physiological 

 action of vegetation." 



The objection urged against the experiments of SCHULZE 

 and SCHWANN, that the air entering the flasks had been 

 affected in some manner by the violent treatment to which 

 it had been subjected, so that it was no longer able to furnish 

 the conditions of growth required by the germs existing in 

 the liquid, was overcome by the beautiful experiments of 

 SCHROEDER and DUSCH (1854), who obtained the same result 

 by allowing the air to pass through cotton-wool filters. 



Finally PASTEUR (1862) showed that, if in some 

 experiments made by the last-mentioned investigators the 

 boiled liquid still contained a growth of living organisms, 

 it was owing to the substance not having been boiled long 

 enough. 



The principles of the whole technology of sterilisation being 



