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: 



(i) 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 



