214 MASS. EXPERIMENT STATION BULLETIN 187. 



time for multiplication, and, further, in the slime large masses of organ- 

 isms are found, this laboratory has felt it desirable, nevertheless, to 

 undertake the determination of the number of organisms in milk before 

 and after clarification, not so much for the purpose of contributing to 

 what has already been given, but rather for the purpose of knowing what 

 is really involved in the determination and what interpretation of the 

 results obtained may be given. Since the operation of clarifying is so 

 short, it is difficult to believe that any multiplication takes place, as has 

 already been stated above. If none takes place then it must be a dis- 

 ruption in colonies, which leads the student to wonder whether there is 

 greater efficiency in micro-organisms liberated from a disrupted colony as 

 compared with the same organisms imbedded in the colony. This will 

 appear later. 



The authors' studies were carried out under the following conditions: — 



The clarifier used was No. 98 De Laval. It was run by a ^-horsepower 

 motor at uniform speed of 7,200 to 7,300 revolutions per minute. The 

 temperature was maintained at 60° C. when clarifjdng. As soon as the 

 machine reached full speed the milk was passed through. The bowls, 

 discs, etc., were sterilized in an autoclave at 15 pounds pressure for thirty 

 minutes. The milk both before and after clarification was thoroughly 

 mixed prior to taking the samples, which were placed in sterile flasks. 



In the case of certified milk, the milk was obtained from the milker in 

 the "certified" stable; in the case of the commercial milk, from the 

 receiving room of the college dairy. The commercial milk came from the 

 farmers in the vicinity of the college, and was not above the average 

 commercial milk. It doubtless reached the clarifier sooner than it would 

 had it been sent to a city from Amherst, then clarified after reaching the 

 city. 



For estimating the number of bacteria in milk, the Standard Methods 

 of the American Public Health Association were employed. An effort 

 was made to adhere to these methods in all of our work so far as 

 feasible. 



A determination of the number of bacteria cast out by the clarifier into 

 the slime has been undertaken both by a direct count, mathematical cal- 

 culation, and by repeated maceration and clarification. Methods and 

 discussion will be reserved until after some facts have been placed before 

 the reader. 



