22 



A. P. H. A. MILK ANALYSIS 



laboratories are, however, using a 

 laboratory method for the elimination 

 of long chain streptococci derived from 

 inflamed udders. Certain precautions 

 must, however, be used in this case as 

 false interpretations of findings are 

 easily possible. The long chain strep- 

 tococci are readily found by microscopic 

 examination of dried films of milk or 

 of sediments from centrifuged samples 

 of milk. Perhaps the two most fre- 

 quently used routine methods are the 

 Breed method already described, and 

 the Stewar.t-Slack method described in 

 detail in the first edition issued by the 

 American Public Health Association^^- 



The use of these methods for this 

 purpose has shown that even the 

 presence of large numbers of long 

 chain streptococci may be of little 

 significance where there has been oppor- 

 tunity for their growth after the milk 

 das been drawn. Streptococci of the 

 long chain type occur frequently in 

 apparently normal udders, and may 

 even occur in very large numbers where 

 threre is no clinical evidence of in- 

 ilammation^^- Nevertheless, where sam- 

 ples of milk can be taken from individ- 

 ual cans as delivered within 6 hours 

 after milking, it has been found that 

 it is almost invariably possible to find 

 a cow suffering from an inflamed udder 

 if the count of individual cocci in 

 long chains is in excess of 1,000,000 

 per cc. Such milk usually contains 

 leucocytes in excess of 1,000,000 per 

 cc. ; but this relationship is not an 

 invariable one. Because of the pres- 

 ence of alkaline substances from blood 

 serum, milk from cows with inflamed 

 udders usually has a pH value greater 

 than 6.8 and may also contain de- 

 tectable mucin fibers'". 



Where milk is centrifuged and the 

 sediment examined, even greater cau- 

 tion should be used in drawing con- 



clusions, as the concentration of ma- 

 terial may cause insignificant numbers 

 of these organisms to be regarded as 

 significant. In this connection it 

 should be remembered that many 

 entirely satisfactory butter starters 

 are composed of streptococci which 

 occur in fairly long chains. These 

 supposedly saphrophytic streptococci 

 cannot be distinguished from the udder 

 streptococci through microscopic ex- 

 amination alone. 



Under these conditions, the lab- 

 oratory findings should in every case 

 be confirmed by clinical examination 

 of suspected herds before action is 

 taken. 



SUMMARY 



In order to separate required pro- 

 cedures from the necessary discussion, 

 a short summary of the former has 

 been prepared as follows: 



Collection of Samples. Milk to 

 be thoroughly mixed, and sampled 

 with a sterile, straight sided tube 

 (thief) long enough to reach to the 

 bottom of the can or bottle. Each 

 sample is to be at least 10 cc. and is 

 to be kept in a tightly stoppered bottle 

 (closure with cotton plugs is not per- 

 mitted). Samples are to be iced and 

 if plates are not made within four 

 hours of the time when the samples 

 were taken, the time elapsing is to be 

 reported. 



MACROSCOPIC colony COUNT (PETRI 

 PLATE method). 



Composition of Medium 

 Agar 1-2% if oven dried, or 



1.5% if undried. 

 Beef extract 0.3% 

 Peptone 0.5% 



Distilled water. 



