74 WHAT IS LIFE 



organisms and it is only a question of time as to 

 when the fluid will " go bad " as we commonly put 

 it. Let, however, such a fluid be boiled for long 

 enough and all the organisms which it contains will 

 have been killed and the fluid rendered temporarily 

 sterile. Now if it is again exposed to the air it 

 will again accumulate bacteria and again commence 

 to decompose. Let us suppose, however, that 

 when the process of boiling has gone on for long 

 enough and the fluid is quite sterile, the neck of 

 the flask in which it has been boiling is hermetically 

 sealed up. No further bacteria can obtain ad- 

 mission and the contents will remain " good " as 

 long as the seal of the neck remains perfect. It is 

 on this experiment that the " canning" trade 

 has been built up and every glass jar of soup or 

 of calves'-foot jelly which we look at in a shop 

 window is a standing proof of the truth of the facts 

 which Pasteur proclaimed. As to the other two 

 experiments, in the one case the bacteria are 

 filtered out of the air mechanically by the wad of 

 cotton-wool. The other is also a case of mechanical 

 separation, for the tubular neck of the vessel being 

 narrow and the bends in it frequent the bacteria 

 become deposited on the sides of the tube before 

 reaching the fluid contained within the flask. As 

 a result of these experiments the view that all 

 living matter is derived from living matter is now 



