MILK 447 



Staphylococcus pyogenes aureus. 



Bacillus enteritidis sporogenes. 



Bacillus diphtherias. 



Bacillus tuberculosis. 



Some of these occur as accidental contaminations, 

 either from the water supply to the cow farm, or from 

 the farm employees, whilst others are derived directly 

 from the cow. 



In milk, as in water examinations, two methods are 

 available, viz.: Enrichment and Concentration the 

 former is used for the demonstration of bacteria of in- 

 testinal origin, the latter for the isolation of the micro- 

 organisms of diphtheria and tubercle. The first essen- 

 tial in the latter process is the concentration of the 

 bacterial contents of a large volume of the sample into 

 a small compass; but in the case of milk, thorough 

 centrifugalisation is substituted for filtration. 



Apparatus Required: 



A large centrifugal machine. This machine, to be of real 

 service in the bacteriological examination of milk, must conform 

 to the following requirements: 



1 . The centrifugal machine must be of such size, and should 



carry tubes or bottles of such capacity, as to enable 

 from 200 to 500 c.c. of milk to be manipulated at one 

 time. 



2. The rate of centrifugalisation should be from 2500 to 



3000 revolutions per minute. 



3. The portion of the machine destined to carry the tubes 



should be a metal disc, of sufficient weight to ensure 

 good "flank" movement, continuing over a con- 

 siderable period of time. In other words, the machine 

 should run down very gradually and slowly after the 

 motive power is removed, thus obviating any dis- 

 turbance of the relative positions of particulate 

 matter in the solution that is being centrifugalised. 



4. The machine should preferably be driven by electricity, 



or by power, but in the case of hand-driven machines 

 (a) The gearing should be so arranged that the 

 requisite speed is obtained by not more than 

 forty or fifty revolutions of the crank handle 

 per minute, so that it may be maintained 

 for periods of twenty or thirty minutes 

 without undue exertion. 



