3G2 LAY SERMONS, ADDRESSES, AND REVIEWS. |xv. 



fected in constituents of the air by the wool, by prov- 

 ing that the cotton-wool might be dispensed with 

 altogether, and perfectly free access left between the 

 exterior air and that in the experimental flask. If the 

 neck of the flask is drawn out into a tube and bent 

 downwards ; and if, after the contained fluid has been 

 carefully boiled, the tube is heated sufficiently to de- 

 stroy any germs which may be present in the air which 

 enters as the fluid cools, the apparatus may be left to 

 itself for any time and no life will appear in the fluid. 

 The reason is plain. Although there is free communi- 

 cation between the atmosphere laden with germs and 

 the germless air in the flask, contact between the two 

 takes place only in the tube ; and as the germs cannot 

 fall upwards, and there are no currents, they never 

 reach the interior of the flask. But if the tube be 

 broken short off where it proceeds from the flask, and 

 free access be thus given to germs falling vertically out 

 of the air, the fluid which has remained clear and desert 

 for months, becomes in a few days turbid and full of 

 life. 



These experiments have been repeated over and 

 over again by independent observers with entire suc- 

 cess ; and there is one very simple mode of seeing the 

 facts for oneself, which I may as well describe. 



Prepare a solution (much used by M. Pasteur, and 

 often called " Pasteur's solution ") composed of water 

 with tartrate of ammonia, sugar, and yeast-ash dis- 

 solved therein. 1 Divide it into three portions in as 

 many flasks; boil all three for a quarter of an hour; 

 and, while the steam is passing out, stop the neck of 

 one with a large plug of cotton- wool, so that this also 



1 Infusion of hay treated in the same way yields similar results ; but, as 

 it contains organic matter, the argument which follows cannot be based 

 upon it. 



