6 THE THEORY OF SPONTANEOUS GENERATION 



may be considered that they were unduly diffident, since the action of the 

 cotton-wool filter proves that this something must necessarily be a solid body 

 and not a gas. But, on the other hand, both investigators could point to experi- 

 ments wherein the previously boiled test liquid afterwards underwent decom- 

 position, notwithstanding the fact that all the air which was allowed access to it 

 had been filtered through cotton-wool. Milk they had, in their first treatise, 

 recognised as such a liquid, and to this were added, in a second communication 

 by SCHRODER (I.), yolk of egg, meat, and meat broth, in all of which cases the 

 filtration of the air proved useless. This led Schroder to separate the pheno- 

 mena of decomposition characterised as fermentation and putrefaction into 

 two groups : the one, which he designated " voluntary decomposition," requiring 

 only oxygen for its inception, whilst the othei", e.g. the fermentation of wort, 

 required, in addition, the collaboration of that unknown constituent of the air, 

 which could be destroyed by fire or arrested by a cotton-wool filter. " Whether 

 this active substance should be regarded as germs floating in the air, or as some 

 hitherto unknown chemical substance modified by high temperature and sepa- 

 rated andi fixed by the influence of contact with the cotton fibres, must remain 

 undecided." 



Glancing back for a moment at the work of Schultze, one would be only too 

 readily disposed to consider the results of Schroder and Dusch's experiment as a 

 retrogade step, since they not only did not afford us any further information 

 beyond that established by Schultze as to the nature of the germs in the air, but 

 also called in question the accuracy of Schultze's results. And, in fact, repeti- 

 tions of the Schultze experiment by many other workers, with various modifi- 

 cations, especially with regard to the kind of test liquid employed, confirmed the 

 results of Schroder and Dusch. In numerous instances decomposition ensued, 

 even in the boiled liquid, when purified air (filtered or heated to redness) alone 

 was 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 spon- 

 taneous 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 proof was 

 not obtained by the methods which had generally been favoured 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 sterilisation 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 temperature 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 spon- 

 taneous 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 



