THE QUESTION OF SPONTANEOUS GENERATION. 103 



exactly as in the case of infusions recently exposed to 

 the contact of ordinary air. 



The same experiments may be repeated with 

 slightly alkaline liquids, such as milk, the precaution 

 being taken of raising them to a temperature higher 

 than that of 100 degrees Centigrade. 



The great interest of Pasteur's method consists in 

 its proving unanswerably that the origin of life, in 

 infusions which have been heated to the boiling point, 

 is solely due to the solid particles suspended in the 

 air. Of gas, electricity, magnetism, ozone, things 

 known or unknown, there is nothing in ordinary 

 atmospheric air which, apart from these solid par- 

 ticles, can cause the fermentation or putrefaction of 

 the infusions. 



Lastly, to convince the most prejudiced minds, 

 and to leave no contradiction standing, Pasteur 

 showed one of these bulbs with the sinuous neck which 

 he had prepared and preserved for months and years. 

 The bulb was covered with dust. ' Let us,' said he, 

 ' take up a little of this outside dust on a bit of glass, 

 porcelain, or platinum, and introduce it into the 

 liquid; the following day you will find that the in- 

 fusion, which up to this time remained perfectly clear, 

 has become turbid, and that it behaves in the same 

 manner as other infusions in contact with ordinary 

 air.' 



If the bulb be tilted so as to cause a little drop 



