CHAPTER XXIV 

 THE MICROBE OF MILK 



MILK,, fresh from the cow, after standing a few 

 hours in warm weather, as every one knows, be- 

 comes sour. The cause of the souring is not in the 

 milk itself. Milk taken from the cow and sealed 

 airtight, without coming in contact with the air, 

 will not sour. This proves that the cause of sour- 

 ing is not in the milk itself. 



Therefore the something which sours the milk 

 must be either the air, with which the milk comes 

 in contact, or that which comes out of the air into 

 the milk. But it is not the air. Fill a small glass 

 jar with sweet milk. Leave out the cork. Set this 

 jar in a larger glass jar. Seal airtight the larger 

 jar. Now set the larger jar in a vessel of water 

 on the stove. Boil the water for some time. This 

 sterilizes the air in the larger jar and the milk, 

 too. The sterilized air within the larger jar comes 

 in contact with the sterilized milk in the smaller 

 jar. But the milk will never sour. This shows 

 that it is not the air which sours the milk, but 

 something within the air which comes from the air 

 into the milk. 



This something is now well known to be the mi- 

 crobe represented in Fig. 61. It resembles the mi- 



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