8 THE THEORY OF SPONTANEOUS GENERATION. 



admitted ; whilst in other cases, under precisely similar conditions, 

 the boiled sample remained unaltered for any length of time. 

 Thus the state of the question at the commencement of the sixth 

 decade was just about as far advanced as at the beginning of the 

 century, and the adherents of the spontaneous generation theory 

 were more certain of triumph than ever. 



7. The Examination of this Theory by Pasteur. 



However, the day of refutation was close at hand, though the 



Eroof was not obtained by the methods which had generally been 

 ivoured hitherto, but which had led to no definite issue. 



Experimenters had so concentrated their attention on keeping 

 the air admitted to the boiled liquid perfectly free from active 

 germs, that it had not occurred to any one to ask if the sterilisa- 

 tion of the liquid could not be equally ensured by simply boiling 

 it, either momentarily or continuously for a short time. 



Reasoning from the fact that all known forms of created life 

 (animal as well as vegetable) were incapable of resisting the tem- 

 perature of boiling water, even when exposed thereto for merely 

 a short time, the conclusion was arrived at that the same effect 

 was produced on the small germs in question. It was therefore 

 considered, humanly speaking, certain, that every liquid could be 

 rendered free from active germs by boiling for a short time. This 

 was agreed to both by those who accepted and by those who 

 rejected the doctrine of spontaneous generation. Still such 

 belief was based on a mere assumption, as CH. BONNET (I.), a 

 contemporary of Spallanzani's, implied when he inserted the 

 following query in his work opposing the theory of spontaneous 

 generation: "Is it, then, certain that there exist no animals or 

 eggs capable of supporting a temperature equal to that of hot ashes 

 without losing their life or reproductive power ? " 



Pasteur called to mind this doubt of Bonnet's when he began 

 to subject the theory of spontaneous generation to experimental 

 examination in response to the offer made in 1860 by the Paris 

 Academy of Science of a prize for " an attempt, by means of suit- 

 able experiment, to throw new light on the question of spontaneous 

 generation." From the report of his researches, which appeared 

 early in the year 1862, in the form of a comprehensive treatise (I.), 

 well deserving perusal, only the most important result can be re- 

 ferred to here: viz., the demonstration of the possibility, by the 

 assistance of sufficiently prolonged heating at an adequately high 

 temperature, of sterilising (i.e. freeing from living germs) any 

 substance whatsoever ; and of the fact that a sample so sterilised 

 will not subsequently undergo decomposition, but will remain 

 unaltered, so long as care is taken to prevent the access of germs 

 from the external air. 



The objection raised by the heterogenists, viz., that decomposi- 



