HOW THE TEST IS MADE 25 
HOW THE BACTERIAL TEST IS MADE 
Milk which is clean and fresh contains very 
small numbers of bacteria. Milk which is dirty 
or stale contains large numbers of bacteria. 
The human eye cannot see a single bacterium be- 
cause it is too small, any more than the hu- 
man eye can see a single grain of wheat in 
the distance. But just as the human eye can 
easily see a whole field of wheat growing, in like 
manner it is easy to see bacteria when they grow 
in large masses. One bacterium will multiply 
into a mass in one or two days big enough to be 
seen with the naked eye. 
The bacterial test of milk as it is carried out 
in milk testing laboratories gives each of the 
bacteria in the milk a chance to produce its own 
mass of descendants, so that these masses may 
be separately counted. 
The test is performed as follows: 
(1) A sample of milk must be taken from the 
farmer’s can into a glass bottle which contains 
no bacteria, because the bottle has been sterilized 
by baking in an oven. The milk must be trans- 
ferred from the farmer’s can to the sample bottle 
most carefully. The thumb or fingers or a dirty 
