386 THE CAUSES OF THE xi 



to you and then finding those extraordinary 

 anomalies, as in the case of the mercury bath and 

 the milk, he set 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 circum- 

 stance, but this very slight degree of alkalinity 

 seems to have the effect of preserving the organ- 

 isms which fall into it from the air from being 

 destroyed at a temperature of 212, which is the 

 boiling point. But if you raise the temperature 

 10 when you boil it, the milk behaves like every- 

 thing 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 mercury 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 circum- 

 stances 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 supplied 

 with the large quantity that had so puzzled him. 



