262 GENEEATION. 



vented, no infusoria were developed ; and this was the case 

 when air was admitted to the infusions, care being taken to 

 pass the air through heated tubes or sulphuric acid, so as 

 to destroy all organic matter. The present aspect of the ques- 

 tion of spontaneous generation is the following : 



First, it is reduced to the very lowest orders of infusoria, 

 such as vibriones and bacteria, which simply present move- 

 ment, have no distinguishable internal structure, and are ex- 

 ceedingly minute. 



Second, the question is discussed as to what degree of tem- 

 perature and length of exposure to heat are necessary in order 

 to destroy preexisting germs in organic infusions ; for the 

 idea that living organisms ever result from an aggregation of 

 inorganic particles has been generally abandoned, and the so- 

 called spontaneous production of animals has been reduced to 

 a coming together of organic molecules. 



It is at once apparent to the rigidly scientific mind that 

 the second division of the question presents great difficulties 

 in the way of its positive solution. It is granted, for ex- 

 ample, that vibriones and bacteria are living, animal organ- 

 isms. It is proposed by the advocates of the theory of spon- 

 taneous generation, that these beings arise without preexist- 

 ing germs, by an aggregation of organic particles. The op- 

 ponents of this view assert that, when the air admitted to 

 organic infusions is freed from germs or organic particles, 

 and when the organic infusions are subjected to a high tem- 

 perature for a time sufficient to destroy all possible preexist- 

 ing germs, no generation of infusoria can take place. Now, 

 what degree of temperature is required, what is the duration 

 of exposure to heat necessary to destroy germs, and how are 

 the limits of these conditions to be ascertained ? J The only 



1 Upon this point, we may refer to the admirable and entirely conclusive ex- 

 periments of Wyman. His conclusions, as far as they bear upon the question 

 under consideration, are the following : 



" 1st. In thermal waters plants belonging to the lower kinds of Algae live hi 

 water the temperature of which in some instances rises as high as 208 Fahr. 



" 2d. Solutions of organic matter boiled for twenty-five minutes, and exposed 



