METHODS OF EXAMINING MILK 279 
sel in which it was collected to the test tube, the necessary 
precautions should be observed to prevent contamination. 
Twelve hours after they are placed in the incubator, 
the samples are examined. If the milk is normal, fresh 
and of good quality, there will be no change apparent ex- 
cept perhaps a clean, sour odor. The beginning of fer- 
mentation or curdling is indicated by an upward bulging 
of the cream layer and the presence of a greenish layer 
beneath it. If there is no change at this time, the samples 
are to be replaced in the incubator and observed again in 
twelve hours, and subsequently at twelve-hour periods if 
necessary. If curdling does not take place after forty- 
eight hours, the reaction of the milk should be taken and 
tests made for preservatives. When the milk curdles, the 
time of curdling and the character of the curd are to be 
noted. The time of curdling depends upon the number of 
bacteria present which are not inert, while the character 
of the curd depends upon the kind of bacteria which pre- 
dominate. The types of curds, the symbols by which they 
are recorded, and their indications are as follows: 
1. Jelly-like Curd.—J,, solid, smooth, white, jelly- 
like curd, with no fluid. J:, curd of same type, but show- 
ing a few furrows or gas bubbles. J;, curd same, but 
showing more furrows and gas bubbles and also cracks, 
with some fluid. The jelly-like curd is produced when 
the acid-forming bacteria predominate, and if the number 
of bacteria is excessive it usually indicates that the milk 
vessels or utensils are unclean, or that the milk is old or 
has not been kept under proper conditions. 
2. Peptonized Curd.—The curd may be firm, jelly- 
like, with ragged surfaces, or it may be soft, flocculent 
or “mushy,” associated in either case with more or less 
fluid. P,, the amount of fluid is small in proportion to 
