12 SELLING MILK 
milk and unclean milk, because they did not know 
how. Some milk drinkers prefer to drink clean 
milk. Cleanliness, therefore, has a market value. 
There would be a market for clean milk if it 
could be identified from the other kind. 
Cleanliness costs money. It costs money to 
keep dairy utensils smooth and in good repair. 
It costs money to wash and sterilize. It costs 
money to brush and wash cows, and clean stables, 
and to wash milkers’ hands. It costs money 
to milk carefully, and to cool milk. 
At last a way has been found to measure 
cleanliness. This measurement consists of test- 
ing milk for bacteria. 
