INTRODUCTION. 13 



and kindness of whose character excite our admiration equally 

 with his devotion to his work* 



Before the nature of fermentation was understood the pos- 

 sibility of spontaneous generation had been universally ad- 

 mitted. When vermin of various sorts appeared in putrefying 

 material the conclusion was draAvn that they had their origin 

 directly from it. Although that had long since been disproved 

 in the case of large organisms like worms and frogs, still, as late 

 as the middle of the last century, it was held by many to account 

 for the swarming microscopic hfe found in fermenting fluids. A 

 flask of meat broth left exposed to the air will after a few days 

 contain countless tiny living things, chiefly bacteria. Pasteur and 

 his supporters showed that these bacteria were the progeny of 

 others already in the flask or which had fallen in from the air. 



When the flask of broth was boiled, no development of or- 

 ganisms took place, if the entrance of germs from the atmosphere 

 was prevented. The latter was accomplished by such devices 

 as heating the air, passing it through sulphuric acid, using a flask 

 with a long twisted neck or by plugging the flask with cotton 

 (Schroder and Von Dusch). 



To prove that bcihng had not made the fluid unfit for the 

 growth of organisms, air was subsequently allowed to have access 

 to it without such precautions, when putrefaction took place in 

 the usual manner. 



At the same time it was demonstrated not only that bacteria 

 are present in all fermenting and putrefying substances, but 

 that they exist wherever there is animal hfe or vegetation. 



These principles underhe the methods used daily for the pres- 

 ervation of meat, fruit and vegetables, in the household and in 

 factories. 



Although even boiling occasionally failed to prevent fer- 

 mentation, investigators came with practice to have a smaller 



• * See Louis Pasteur. His Life and Labors. By His Son-in-Law. Translated 

 by Lady Claude Hamilton. 



