PUBLIC PROBLEMS 



175 



perature of 98. With this method the plates may be counted 

 in 24 hours, and the number of bacteria in the original sample 

 of milk determined. 



The method of testing by the microscope, given on page 285, 

 is adopted in some places with success, and gives a very much 



FIG. 58 COLLECTING CASE FOR MILK SAMPLES 



The samples are removed from the cans with sterilized pipettes, and placed in 

 tubes. These are placed in weighted racks (A) and put into the center 

 compartment of the carrying case. 



more rapid method of determining whether the sample of milk 

 has such a small number of bacteria in it that it falls below a 

 standard of 500,000 per c.c., or whether the number is so large 

 as to run far beyond this. By the culture method at least 24 

 hours must elapse; by the microscopic method the results are 

 fairly quick. In using the microscopic method it is desirable, 

 if the microscope shows that the number of bacteria is probably 

 in the vicinity of the 500,000 limit, to make agar plates at onre 

 in order that the test of the microscopic method may be con- 



