284 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



within the limits set for normal milk, the possible pres- 

 ence of mastitis secretion is not excluded. 



The presence of numerous streptococci in connection 

 with an excess of leucocytes is strong evidence that the 

 milk contains secretion from an inflamed udder. Milk 

 may contain non-pathogenic (Streptococcus lacticus) as 

 well as pathogenic streptococci but, as was first pointed 

 out by Bergy, the streptococci may be regarded as path- 

 ogenic when they are associated with a large number of 

 polymorphonuclear leucocytes, especially if they are in 

 long chains. The presence of cocci, diplococci, or short 

 chains within the cells is also significant. Furthermore, 

 the pathogenic streptococci usually form longer chains 

 than the non-pathogenic, chains of Streptococcus lacticus 

 rarely containing more than 6 or 8 organisms. (See 

 Figs. 5 and 6) . According to Ernst, the mastitis strep- 

 tococci can be recognized by the shape of the individual 

 cocci and the length of the chain. ( See page 53. ) 



The leucocyte tests are more reliable for individual 

 milk than for market milk. In comparisons of the leuco- 

 cyte tests with the catalase test in the examination of in- 

 dividual milk to discover evidence of mastitis, the catalase 

 test has proven the more accurate. 



BOILING TEST 



A small quantity of milk is placed in a vessel and 

 boiled, after which it is examined for flakes or curds. In 

 the laboratory, about 10 to 15 c.c. of milk is placed in a 

 test tube, which is then held over a Bunsen flame until the 

 milk boils. Fresh, normal market milk will not curdle. 

 When curdling occurs, it indicates that the milk has un- 

 dergone excessive acid fermentation, either because it is 

 stale, or was produced under unclean conditions, or was 



