74 ORIGINATION OF LIVING BEINGS. 



taming the infusion into the mercury, so that the latter 

 reached a little beyond the level of the mouth of the 

 invei'ted vessel. You see that he thus had a quantity 

 of the infusion shut off from any possible communica- 

 tion 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- 

 fectly pure atmosphere of the same constituents as the 

 external air. Of course, he expected he would get no 

 infusorial animalcules at all in that infusion ; but, to 

 his great dismay and discomfiture, he found he almost 

 always did get them. 



Furthermore it has been found that experiments 

 made in the manner described above answer well with 

 most infusions ; but that if you fill the vessel with 

 boiled milk, and then stop the neck with cotton-wool, 

 you will have infusoria. So that you see there were 

 two experiments that brought you to one kind of con- 

 clusion, and three to another ; which was a most un- 

 satisfactory state of things to arrive at in a scientific 

 inquiry. 



Some few years after this, the question began to be 

 very hotly discussed in France. There was M. Pouchet, 

 a professor at Rouen, a very learned man, but certainly 

 not a very rigid experimentalist. lie published a num- 

 ber of experiments of his own, some of which were very 

 ingenious, to show that if you went to work in a proper 

 way, there was a truth in the doctrine of spontaneous 

 generation. Well, it was one of the most fortunate 

 things in the world that M. Pouchet took up this ques- 



