486 ON THE CAUSATION OF 



freely exposed to the atmosphere ; and also that the essential source of such 

 development must be suspended particles or germs. But in order to render the 

 experiment, if possible, still more conclusive, the Committee of the Academy 

 completed it by sealing the end of the neck of the flask, after the fluid had re- 

 mained clear for a sufficient length of time to show that no organisms could grow 

 in it, and inverting and shaking the vessel till some of the liquid passed into the 

 angles of the bent tube, after which the flask was again left to itself. And now, 

 gentlemen, occurred something which you may perhaps be disposed to regard as 

 too good to be true, but which is true nevertheless. In the course of no long 

 time the fluid in the angles of the tube exhibited indications of organic growth, 

 demonstrating that the sources or germs of such development had, as a matter 

 of fact, been arrested there. 



This experiment charms us alike by its simplicity and perfect conclusiveness. 

 Here is evidence indeed, which, if the facts be admitted, cannot be gainsaid. 

 But though I could not doubt the authority on which it rested, I felt desirous, if 

 possible, to bring it to bear more directly upon the subject of putrefaction. The 

 fluid which seemed most likely to answer the purpose, combining transparency 

 with a high degree of putrescibility, was urine, and I accordingly made it the sub- 

 ject of the experiment to which I now desire to direct your attention.^ Two 

 years ago last month, I introduced portions of the same specimen of fresh urine 

 into four flasks, of which two are before you. The body of each vessel was about 

 one-third filled with the liquid. After the introduction of the fluid, the necks 

 of three of them were drawn out into tubes rather less than a line in diameter, 

 and then bent at various acute angles, as 3'ou observe in one of these. In the 

 other the neck was drawn out to a calibre if anything rather finer, but cut short 

 and left vertical, as you see it. The liquid in each flask was then boiled for five 

 minutes, the steam issuing freely from the open end of the narrow neck. The 

 reason for boiling it so long is that, as Pasteur has shown, merely raising this 

 fluid to the temperature of 212° Fahr., and then allowing it to cool, is not enough 

 to kill all the organisms it may contain. It is necessary to maintain the elevated 

 temperature for about five minutes to ensure complete destruction of their 

 vitality.- The lamp being then removed, air of course passed in to take the place 

 of the condensed aqueous vapour. And during the two years that have since 



* Since making the experiment I have learned that Pasteur had previously performed it \vith urine. 



'^ See Comptes Rendus, vol. 1, p. 306. It follows that if any germs were drawn into the body of 

 the flask with the air that rushes in on the withdrawal of the lamp, they would retain their vutaUty in 

 the hot liquid, and develop in it when it had cooled. I have elsewhere expressed the opinion that the 

 germs contained in the air which is thus rapidly admitted in the first instance must be arrested by the 

 drops of water wliich appear in the angles of the tube immediately on the cessation of ebulhtion, just as 

 the particles of dust in inspired air are stopped by the mucus of our bronchial tubes. See British 

 Medical Journal, July 18, 1868 (page 58 of this volume). 



I 



