10 MICRO-ORGANISMS AND FERMENTATION. 



had been given in the old experiments on spontaneous 

 generation. 



As early as the year 1765, Spallanzani argued against the 

 doctrine of Needham and Buffon, that living beings came 

 into existence through spontaneous generation in putrefying 

 liquids or other substances. SpaUanzani warmed extract of 

 meat in closed flasks, and demonstrated that the contents 

 of the flasks remained unaltered until air is allowed to 

 gain admittance. From this he concluded that the germs 

 which developed in the opened bottles had come in from the 

 air. Later (1782) Scheele demonstrated that vinegar may 

 be made to keep sound by means of warming. But his 

 discovery was not heeded. In 1810 Appert published his 

 book on a means of preserving various foods and liquids 

 through warming. In the 4th 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 in our day (the so-called " Pas- 

 teurisation " ). 



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

 tance for micro-biology, belong the highly meritorious 

 researches of F. Schulze and Th. Schwann, in which it was 

 shown, that perishable liquids which had been vigorously 

 boiled in flasks would remain sterile if the air subsequently 

 entering were made to pass through sulphuric acid or through 

 red-hot tubes. At the same time Cagniard-Latour and 

 Schwann described the yeast-cells, and Kutzing the acetic 

 acid bacteria. Turpin started (1838) that most important 

 doctrine : " No decomposition of sugar, no fermentation 

 without the physiological action of vegetation." 



Finally, the objection 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 submitted, 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 



