PASTEUR^ ON SPONTANEOUS GENERATION. 119 



were brouglit into contact with pure oxygen or with 

 common air^ even in a scarcely perceptible quantity. 



These experiments^ which have only a comparative exact- 

 ness, have never been contested. By degrees, without 

 bringing to these delicate researches all that critical pre- 

 cision Avhich they demand, authors have extended the prin- 

 ciples of Gay-Lussac to the organisms which arise in infusions ; 

 and at the present day, every one, partisan or opponent of 

 spontaneous generation, admits that the smallest possible 

 quantitj^ of common air brought in contact with an infusion 

 causes, in a short time, the birth of Mucedinece or of Infu- 

 soria. 



This opinion has always been sustained, at any rate indi- 

 rectly, by the habit followed and considered indispensable by 

 observers, of preventing, with infinite precautions in all their 

 experiments, the access of atmospheric air. Sometimes they 

 recommend its calcination ; sometimes its subjection to the 

 most active chemical agents ; frequently they begin by passing 

 it through the vapour of water at 312°; lastly, they operate 

 at other times with artificial air : and should it happen, under 

 any one of these various conditions, that the experiment 

 results in the production of organisms, they do not hesitate 

 to aflirm that the experimenter has been unable completely to 

 avoid the introduction of a small quantity of common air, 

 however minute it may be. Whence the partisans of spon- 

 taneous generation hasten to remark, and not without reason, 

 that if the minutest portion of ordinary air develops organisms 

 in any kind of infusion, this must arise, if the organisms are 

 not spontaneous, from the circumstance that the minute por- 

 tion of air in question contains the germs of a multitude of 

 different productions; and lastly they say, if this be the 

 case, the atmospheric air, to use M. Pou chefs expression, 

 must be loaded with organic matter enough to render it 

 foggy. 



This reasoning, it must be confessed, is very sensible, and 

 the more so since all the lower species which appear to be dis- 

 tinct seem really to be so, and consequently to be derived 

 from different germs. Here then we are met with a serious 

 and, to all appearance, a real difficulty. But is it not an 

 exaggeration, and a deduction from facts more or less erro- 

 neous ? Is it true, as is presumed since Gay-Lussac, that 

 the cause of the so-termed spontaneous generation is con- 

 stantly in operation in the atmosphere ? Is it quite certain 

 that the smallest quantity of common air does suffice for the 

 development of organized productions in any kind of infusion? 

 Lastly, what amount of confidence can be placed in Gay- 



