330 THE CANADIAN NATURALIST. [Sept. 



sowing them in a solution fitted for their developement. And, 

 thirdly, he showed that the incapacity of'air strained through cotton- 

 wool to give rise to life was not due to any occult change effected 

 in constituents of the air by the wool, by proving 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 down- 

 wards, and if, after the contained fluid has been carefully boiled, 

 the tube is heated sufficiently to destroy 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 communica- 

 tion 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 V7ith entire success; and there is one very 

 simple mode of seeing the fact 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 dissolved therein. 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. 

 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 

 may be thoroughly steamed. Now set the flasks aside to cool, 

 and when their contents are cold, add to one of the open ones a drop 

 of filtered infusion of hay which has stood for twenty -four hours, 

 and is consequently full of the active and excessively minute 

 organisms known as Bacteria. In a couple of dayg of ordinary 

 warm weather, the contents of this flask will be milky, from the 

 enormous multiplication of Bacteria. The other flasks, open and 

 exposed to the air, will, sooner or later, become milky with Bac- 

 teria, and patches of mould may appear in it ; while the Hquid in 



