HOW THE TEST IS MADE 29 



(6) The dishes are put in an incubator where 

 the temperature is the same as that used in 

 hatching hens' eggs. They remain there for two 

 days. 



COLONIES OF BACTERIA 



The jelly is perfectly clear at first. After 

 two days there are developed white and gray spots 

 on the jelly where the bacteria in the milk have 

 grown into masses. Each germ has surrounded 

 himself with millions of descendants, making a 

 spot visible to the naked eye. It is easy to 

 count these spots, and thus count the number 

 of bacteria present in the milk sample. The 



