272 the president's address. 



It follows inevitably from the above considerations that the 

 frequent failure of experimenters to demonstrate the occurrence 

 of spontaneous generation cannot be regarded as proof that it 

 never takes place even at the present day ; much less as proof 

 that it has never taken place in the past. 



The classical experiments of Pasteur, Tyndall and other 

 observers of the nineteenth century, so far as they related to 

 spontaneous generation, seem to have been for the most part 

 confined to the problems involved in the occurrence of organisms 

 in organic infusions, such infusions being the media in which 

 most of the known micro-organisms naturally occur and from 

 which they derive their food-supplies. As a result of such 

 experiments it is generally believed to have been demonstrated 

 clearly enough that if adequate measures are taken in the first 

 place to sterilise the culture media by heat, and in the second 

 place to prevent the access of living germs after sterilisation 

 has been effected, such infusions may be kept for an indefinite 

 time without any organisms making their appearance in them, 

 and, consequently, without undergoing putrefaction. It is also,. 

 I believe, generally supposed, though with little justification, 

 that this conclusion applies to all culture media whatever, 

 whether organic or inorganic. 



One observer, however, Dr. Charlton Bastian, whose earlier 

 experiments were contemporary with those of Pasteur and 

 Tyndall, and who has recently been again engaged in similar 

 investigations, has consistently maintained a different view. 

 His earlier experiments, like those of other observers, were con- 

 ducted with organic infusions, or with artificial nutrient solutions 

 such as ammonium tartrate or other salts of ammonia. The 

 positive conclusions arrived at by experiments with organic 

 culture media may be considered to have been completely nega- 

 tived by the general experience of bacteriologists during the 

 subsequent forty years. 



With regard to the origin of living things from the inorganic 

 world, however, the negative results obtained by properly con- 

 ducted experiments with organic infusions are of comparatively 

 little value. If spontaneous generation takes place at all at 

 the present day it probably takes place as it must have done 

 at some time in the past, when no organic bodies existed to 

 supply food for the first living things. In other words, we 



