ORIGINATION OF LIVING BEINGS. 75 



mouth of the vessel with a red-hot tube in such a way 

 that the air would have to pass through the tube 

 before reaching the infusion, that then you would get 

 no animalcules. Yet another thing was noticed : if you 

 took two flasks containing the same kind of infusion, 

 and left one entirely exposed to the air, and in the 

 mouth of the other placed a ball of cotton wool, so 

 that the air would have to filter itself through it be- 

 fore reaching the infusion, that then, although you 

 might have plenty of animalcules in the first flask, 

 you would certainly obtain none from the second. 



These experiments, you see, all tended towards one 

 conclusion — that the infusoria were developed from 

 little minute spores or eggs which were constantly 

 floating in the atmosphere, and which lose their power 

 of germination if subjected to heat. But one observer 

 now made another experiment, which seemed to go 

 entirely the other way, and puzzled him altogether. 

 He took some of this boiled infusion that I have 

 been speaking of, and by the use of a mercurial 

 bath — a kind of trough used in laboratories — he deftly 

 inverted a vessel containing the infusion into the 

 mercury, so that the latter reached a little beyond the 

 level of the mouth of the inverted vessel. You see 

 that he thus had a quantity of the infusion shut off 

 from any possible communication with the outer air 

 by being inverted upon a bed of mercury. 



He then prepared some pure oxygen and nitrogen 

 gases, and passed them by means of a tube going from 

 the outside of the vessel, up through the mercury into 

 the infusion; so that he thus had it exposed to a per- 



