BACTERIA IN THE INDUSTRIES 199 



(2800 revolutions per minute) hand centrifuge is required. Ice creams, 

 creams, sweetened evaporated milks, must be suitably diluted (1-5 as a 

 rule) before centrifuging in order to facilitate the separation of the bacteria 

 and organic debris and the butter fat. In case of sweetened evaporated 

 milks, the dilution must be sufficient to dissolve all of the lactose and 

 added sucrose. To hasten the solution of the lactose, heat may 

 be employed. 



Place 10 cc. of the milk or the dilutions thereof in special two part 

 (i cc. +9 cc.) tubes and centrifuge for ten minutes. Remove the i cc. 

 end tube, holding the sediment, and mix the contents thoroughly and 

 from this make the bacterial counts, using dilutions as may be required. 



The coccus forms and other microorganisms in heat sterilized milks 

 have lost much of their original staining properties. Dead bacteria 

 generally, especially those killed by moist heat, as a rule, react feebly with 

 the usual stains. The streptococcus form found in evaporated canned 

 milk most generally seen, appears to have the morphological characteristics 

 of the Streptococcus acidi lactici of Kruse, which is believed to be entirely 

 harmless to man and to be in normal lactic acid fermentation of milk. 

 It is, however, quite immaterial from the standpoint of the purity and 

 freshness of milk, whether the organisms found are harmless or not. 



In numerous samples of canned milk where the coccus forms were 

 counted, the numbers ranged from 15,000,000 to 200,000,000 per cc. and 

 over, and the coccus count as a rule exceeded the sum of the diplobacillus, 

 diplococcus and streptococcus counts in the ratio of 4:3. 



Based upon the examination of numerous samples of several brands 

 of evaporated skimmed milks, a count of 100,000,000 pair per cc. of 

 diplo. forms, as a rule, corresponds to about 150,000,000 coccus forms, 

 per cc. or a total of 250,000,000 microorganisms per cc. There appears to 

 be no fixed number ratio between coccus and diplo. forms on the one hand 

 and streptos. on the other, hence the suggestion that these groups be 

 given separate rating values. 



4. Municipal Milk Scoring. In addition to a score card which indi- 

 cates the condition of the dairying establishment and which score will 

 indicate whether or not the owner of the dairy is complying with the re- 

 quirements of the city ordinance, the laboratory analysts are required to 

 make examinations and fill out report blanks, after the following. 



A. TABLE FOR SCORING CHEMICAL EXAMINATIONS OF MILK 



Total solids; Score 100 



13.2 % or more 



For each .1 % under 13.2 % deduct 2 points on score. 

 For added water, deduct 100 points. 



If per cent, of butter fat is less than 3 %, deduct 100 points. 

 For milk containing preservatives, deduct 100 points. 



