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 
