46 SOURCE OF BACTERIA IN MILK. 



tamination. The number of bacteria found in milk at the 

 close of the milking is directly dependent upon the conditions 

 of cleanliness, and one may, within narrow limits, deter- 

 mine the extent of precautions that are taken by the dairy- 

 man in his dairy by a simple quantitative examination of the 

 number of bacteria contained in the fresh milk. If the num- 

 ber is not more than two to three thousand it may be assumed 

 that the condition of the dairy, of the milking vessels, and of 

 the cows is very good. If the number is less than this it indi- 

 cates an exceptionally good condition; if the number is 

 twenty thousand, or more, the indications are that the condi- 

 tions are rather uncleanly. 



It is, however, necessary to remember that the contamina- 

 tion of milk during the milking is subject to great irregulari- 

 ties which are quite beyond explanation at the present time. 

 It occasionally happens that a dairy that is kept in excellent 

 condition and produces milk containing a comparatively 

 small number of bacteria, will suddenly, for some unexplained 

 reason, produce milk of a very different character. In a 

 single experiment, for example, a careful record of the bac- 

 teria in the milk of a well-kept dairy was made for some 

 months. During that period the number of bacteria in the 

 fresh milk ranged from 1,000-10,000 per c.c., and month 

 after month this number was tolerably constant. Suddenly, 

 upon a single day, there was obtained a sample of milk 

 drawn under identical conditions, so far as could be deter- 

 mined, which showed at the outset 400,000 bacteria per 

 cubic centimeter. This milk soured and curdled within 

 eighteen hours, whereas the samples of previous weeks had 

 been easily kept two days without difficulty. What sudden 

 incident produced this extraordinary change it was quite im- 

 possible to determine, for, so far as the dairyman who was 

 carrying on the experiments could determine, there was no 

 difference of conditions in the milk drawn upon this day and 

 previous days. This high number of 400,000 per c.c. was 



