272 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



of the other ; but a few suggestions will give a fairly sat- 

 isfactory idea as to how the two may be related. 



"Grade A raw milk, which should have less than 100,- 

 000 bacteria per c.c., will not show more than three to four 

 small clumps of bacteria for each 30 fields of the micro- 

 scope where the diameter of the fields is .205 mm. Such 

 milk also ought not to contain more than 500,000 individ- 

 ual bacteria per c.c. when counted by the microscope. 

 For Grade A pasteurized milk (which should have less 

 than 200,000 per c.c. by the plate count before pasteuri- 

 zation) the microscope should not show more than six to 

 eight clumps per 30 microscopic fields, and not more than 

 1,000,000 individual bacteria when counted with the 

 microscope. 



"Grade B milk, which is supposed not to have more 

 than 1,000,000 bacteria before pasteurization, when 

 counted by the plating method, should not show more 

 than 20 individual bacteria per field, where the diameter 

 of the fields is .205 mm., and not more than three to four 

 groups of bacteria per field. 



"While the above relation between the plate count 

 and the microscopic counts cannot be relied upon as hav- 

 ing a very great amount of accuracy, it will serve to give 

 a general idea of the ratio between the two under or- 

 dinary conditions, and may serve as a guide in the use of 

 the direct microscopic method." 



EXAMINATION FOR STREPTOCOCCI 



When long-chain streptococci are found in milk sedi- 

 ment in association with an excess of leucocytes and the 

 latter cells are clumped together and consist largely of 

 the polymorphonuclear type, there need be no hesitancy 

 in concluding that the streptococci are pathogenic and 



