A COMBAT WITH AN INFECTIVE ATMOSPHERE. 647 



be utterly unworthy were I not prepared to trample all influences and 

 motives such as those mentioned under foot, and were I not ready, 

 did I conceive myself to be in error in what was brought before you 

 last year, to avow here frankly and fully in your presence that error. 

 I should be unworthy of the title of a scientific man if my spirit had 

 not been so brought into this state of discipline as to be able to make 

 such an avowal. Why, then, do I not accept those results as proving 

 the doctrine of spontaneous generation ? The celebrated argument 

 of Hume comes into play here. When I looked into all my antecedent 

 experience, and into the experience of other men for whoin I have the 

 greatest esteem as investigators, it was more easy for me to believe 

 the error of my manipulation, to believe that I had adopted defective 

 modes of experiment, than to believe that all this antecedent experi- 

 ence was untrue. It was my own work that was thus brought to the 

 bar of judgment, and my conclusion was, that I was far more likely 

 to be in error than that the great amount of evidence already brought 

 to bear upon the subject should be invalid and futile. Hence, instead 

 of jumping to the conclusion that these were cases of spontaneous 

 generation, I simply redoubled my efforts to exclude every possible 

 cause of external contamination. This was done by means of doing 

 away with the pipette altogether and using what we call a separation- 

 funnel. Here you have a chamber with a pipette entering. This 

 pipette-tube has not a bulb or mouth such as you have here ; it is 

 simply closed by a tube of India-rubber, and that again is closed by 

 a pinchcock. Now, here we have an infusion of hay. At present 

 this stopcock stops it. I turn it on ; it goes down ; I turn it off, and 

 this liquid column is now held by atmospheric pressure. This was 

 introduced into the India-rubber tube, the India-rubber tube being 

 first filled with the infusion, so that no bubble of air could get in. 

 When the separation-funnel was placed thus and the cock was turned 

 on, the liquid was introduced into the chamber without an associated 

 air-bubble. Mr. Cotterell will show you the result of this severe ex- 

 periment. Here is an infusion of cucumber, the most refractory of all 

 infusions that I have dealt with. It was prepared on December 8, 

 1876, so that it is between six and seven weeks old. Two days were 

 sufficient to break down this infusion when contamination attacked it; 

 but, by this more severe experiment, it is enabled to maintain itself 

 as clear as crystal, although it has been there for six or seven weeks. 

 You will see by the light behind that it is, as I have described imper- 

 fectly clear. You will observe that the infusion is diminished by 

 evaporation, but it is as clear as distilled water, and there it remains 

 as the result of this severe experiment. 



Let us now ask how it is that these curious results that I have 

 brought before you were possible ; how it is that the results of this 

 year differ so much from those obtained previously. The investiga- 

 tion of this point is worthy of your gravest attention. I am now 



