MILK 93 



B. Estimation of the Number of Bacillus colt and allied 



Organisms. 



The general principles and most suitable methods have been 

 discussed in Chapters I and II so that only any special modifica- 

 tions for milk samples require to be considered. 



The methods to use differ in no way from those employed 

 for water samples except in regard to the dilutions to add to the 

 tubes of lactose bile salt broth. 



Definite fractions of milk are added by pipette, the amounts 

 depending upon the suspected degree of pollution of the milk. 

 A usual procedure is to add ro, 0*1, croi c.c. if the sample is 

 byre milk, and if it is ordinary vended milk to add, in addition, 

 O'OOi,O'OOOi,O'OOOOi, O'oooooi c.c. and occasionally even smaller 

 fractions. The dilutions are obtained as described above. 



The B. coli group organism is isolated from the smallest 

 amount giving gas and acid after incubation at 37 C. for 

 two days. 



These dilutions are widely spaced, and consequently the 

 number of B. coli present can only be enumerated between 

 rather wide limits. The writer prefers therefore to add several 

 equal amounts to lactose bile salt broth tubes. Thus for samples 

 collected at the byre he adds I c.c. to each of five broth tubes 

 and O'l c.c. to two others, while for ordinary vended milk samples 

 greater dilutions are used, i.e. O'oooi c.c. four, O'OOi c.c. four, 

 O'Oi one, and O'l one. 



By this procedure a much closer estimate of the number of 

 B. coli can be obtained than by the ordinary methods and with 

 but very little more expenditure of time and material. 



C. Estimation of the Niimber of B. enteritidis sporogenes 



Spores. 



The milk itself is directly incubated. The usual quantities 

 of milk to examine are i, 10, and 20 c.c., the smallest amount 

 being added to a tube of freshly sterilized whole milk, while 

 the other quantities are placed in empty sterile test tubes. The 

 milk tubes are heated in a water-bath to 80 C., and kept at that 



