126 MILK TRADITIONS 
raises the temperature of the night’s milk so 
that the mixture is warm enough to allow bac- 
teria to grow. There is no reason why a farmer 
should not mix morning’s and night’s milk if 
he can keep them both cold. At the shipping 
station both morning’s milk and night’s milk 
are usually mixed by the milk deale:, because 
the dealer immediately cools the mixture and 
puts it through his pasteurizer. If milk is kept 
clean and kept cold, it makes little difference 
whether it is morning’s milk or night’s milk or a 
mixture of morning’s milk and night’s milk. 
THUNDERSTORMS 
It is believed by many that milk which was 
sweet before a thunderstorm will be sour after 
a thunderstorm, because of some influence, per- 
haps the influence of electricity on the milk. 
The truth is that the souring can be due only 
to lactic acid produced by the growth of lactic 
acid bacteria. These bacteria cannot grow well 
in cold milk. They will grow well when milk 
is not kept sufficiently cool. Since thunder- 
storms come in hot weather, and hot weather 
often interferes with the proper cooling of milk, 
