INTRODUCTION. 13 



than thirty years. Prominent among those who contended 

 against the agency of living cells in the production of fermenta- 

 tion was Liebig, but in spite of this the doctrine steadily gained 

 ground, and was extended to include other sorts of fermenta- 

 tion and the putrefaction of albuminous material. Different 

 kinds of fermentation, with different products, such as acetic 

 acid and butyric acid, were eventually shown to be due to the 

 growth of different kinds of microbes. 



These microbes were found to be fungi of various sorts, and 

 chiefly one or another variety of bacteria. The most cele- 

 brated among the students of fermentation was Pasteur, the 

 simplicity and kindness of whose character excite our admira- 

 tion 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 drawn 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 life 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 followers 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 atmos- 

 phere 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). 



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

 by Lady Claude Hamilton. 



