ORIGINATION OF LIVING BEINGS. 77 



himself to work to discover their nature. In the case 

 of milk he found it to be a question of temperature. 

 Milk in a fresh state is slightly alkaline ; and it is a 

 very curious circumstance, but this very slight degree 

 of alkaliuity seems to have the effect of preserving the 

 organisms which fall into it from the air from being 

 destroyed at a temperature of 212°, which is the boil- 

 ing point. But if you raise the temperature 10° when 

 you boil it, the milk behaves like everything else ; and 

 if the air with which it comes in contact, after being 

 boiled at this temperature, is passed through a red-hot 

 tube, you will not get a trace of organisms. 



He then turned his attention to the mercury bath, 

 and found on examination that the surface of the mer- 

 cury was almost always covered with a very fine dust. 

 He found that even the mercury itself was positively 

 full of organic matters; that from being constantly 

 exposed to the air, it had collected an immense number 

 of these infusorial organisms from the air. Well, 

 under these circumstances he felt that the case was 

 quite clear, and that the mercury was not what it had 

 appeared to M. Schwann to be, — a bar to the admission 

 of these organisms ; but that, in reality, it acted as a 

 reservoir from which the infusion was immediately sup- 

 plied with the large quantity that had so puzzled him. 



But not content with explaining the experiments of 

 others, M. Pasteur went to work to satisfy himself 

 completely. He said to himself : " If my view is right, 

 and if, in point of fact, all these appearances of spon- 

 taneous generation are altogether due to the falling of 

 minute germs suspended in the atmosphere, — why, I 



