SPONTANEOUS GENERATION. 313 



that no bacteria appeared in the solution after long 

 exposure to the air, the inference was drawn that neither 

 bacteria nor their germs existed in the air. Through- 

 out Germany the ablest literature of the subject, even 

 that opposed to heterogeny, is infected with this error ; 

 while heterogenists at home and abroad have based upon 

 it a triumphant demonstration of their doctrine. It is 

 proved, they say, by the deportment of the mineral 

 solution that neither bacteria nor their germs exist in 

 the air ; hence, if, on exposing a thoroughly sterilized 

 turnip-infusion to the air, bacteria appear, they must of 

 necessity have been spontaneously generated. In the 

 words of Dr. Bastian : ' We can only infer that whilst 

 the boiled saline solution is quite incapable of engen- 

 dering bacteria, such organisms are able to arise de novo 

 in the boiled organic infusion.' ^ 



I would ask my eminent colleague what he thinks 

 of this reasonino- now? The datum is — 'A mineral 

 solution exposed to common air does not develope 

 bacteria ; ' the inference, is — ' Therefore if a turnip- 

 infusion similarly exposed develope bacteria, they must 

 be spontaneously generated.' The inference, on the face 

 of it, is an unwarranted one. But while as matter of 

 logic it is inconclusive, as matter of fact it is chimerical. 

 London air is as surely charged with the germs of 

 bacteria as London chimneys are with smoke. The 

 inference just referred to is completely disposed of 

 by the simple question : ' Why, when your sterilized 

 organic infusion is exposed to optically pure air, should 

 this generation of life de novo utterly cease ? Why 

 should I be able to preserve my turnip-juice side by 

 side with your saline solution for the three hundred and 

 sixty-five days of the year, in free connexion with the 

 .general atmosphere, on the sole condition that the 

 ' Proceedings of the Royal Society, vol. xxi. p. 130, 



