824 TEE POPULAR SCIENCE MONTHLY. 



duction, but proceeds from some previously existing life or parent. 

 Hence, he has held, and has aimed to show, that fermentation can 

 never take place if all access of germs to a fermentable substance is 

 prevented. From fermentation he has extended his theory of the 

 agency of microscopic organisms in working changes, to the explana- 

 tion of tbe origin and multiplication of various infectious diseases, 

 each of which, as well as each kind of fermentation and putrefaction, 

 is caused by its own specific organism. 



M. Pasteur took a prominent and most active part in the contro- 

 versy respecting spontaneous generation, which raged quite bitterly a 

 few years ago. He performed the most decisive experiments that 

 were made, and has contributed more than any other person to turn 

 the current of scientific thought against that theory, and to bring the 

 weight of opinion in favor of his own theory of panspermy. The con- 

 troversy on this subject, which had been resting for many years after 

 the researches of Siebold, Leuckart, and others, into the mode of devel- 

 opment of sexless parasites, was reopened as to the infusoria in 1858 

 by Pouchet, who affirmed that previous experiments in regard to boiled 

 infusions were inexact, and that boiling did not prevent the appear- 

 ance of infusorial life, as it would necessarily do if such appearance 

 was dependent on the existence of living organisms or germs in the 

 liquids previous to boiling. M. Pasteur, having become interested in 

 this subject through his studies in fermentation, came forward with 

 his test experiments. The question seemed a very difficult one, and 

 incapable of a definite solution, so that Pasteur's friends, Biot and 

 Dumas, were impelled to counsel him against wasting too much time 

 upon it. They had, however, good reason afterward to revise their 

 opinions. M. Pasteur boiled a suitable organic infusion in glass flasks, 

 which ho sealed hermetically while the boiling was going on, so as to 

 exclude the air that might bring in new germs to take the place of 

 those which the boiling had killed. The flasks were then taken to 

 different localities, where, after a time, the necks were broken and air 

 was admitted to the boiled infusion. Pasteur reasoned that if the 

 organisms, which were produced in the liquid on exposure to the at- 

 mosphere, were spontaneous growths excited to life by the action of 

 the atmosphere alone, the products would be the same wherever the 

 bottles were broken ; but if the manifestation of life depended upon 

 the introduction of new organisms or their jrerms from the air since 

 the air of different places would probably contain different organisms and 

 be charged in different proportions with them there would be differ- 

 ent results in different places. The experiments showed manifest differ- 

 ences, in accordance with Pasteur's anticipations, and were considered 

 to demonstrate the existence in the atmosphere of extraneous particles, 

 the introduction of which into an infusion was the necessary condition 

 of life nppoaring there. Professor Tyndall says of them that they, " car- 

 ried out with a severity perfectly obvious to the instructed scientific 



