^38 MILK AND THE PUBLIC HEALTH chap. 



To avoid injustice in framing practical working standards it 

 is necessary not only to have separate standards for byre and 

 for vended milk, but these also must be varied for summer and 

 winter. The following are suggested as useful working standards. 



Lactose Fermenters of coli type per c.c. 



B. enteritidis sporogenes spores. — The standards suggested 

 are — good, or 1 (i.e. all 10 tubes negative or only 1 posi- 

 tive) ; unsatisfactory , 2, 3, or 4 tubes positive ; lad, 5 or over 

 positive. Eigid standards for the spores of this organism can- 

 not be set up, while the results are chiefly confirmatory of the 

 lactose fermenters estimation. The one standard is equally ap- 

 plicable to vended and byre milk, and to all times of the year. 



To use the above standards the method of examination to 

 determine the number of lactose fermenters must be defined. 

 The following is suggested. 



Byre Milk — 



Add 1 c.c. of milk to each of 5 L.B.B.i tubes. 

 5) O'l ,, „ 2 ,, 



Incubate all 7 tubes at 37° C. for two days, and record as 

 positive all the tubes showing acid and gas. If the results 

 obtained pass the standard, the presumptive tests are sufficient. 

 If they transgress, the tubes containing the least milk yielding 

 a positive result can, if considered necessary, be plated, and the 

 B. coli or other lactose fermenting organisms isolated. 



Vended Milk. — Make dilutions A, B, C, D, as described in 

 Chapter IX. Inoculate 10 L.B.B. tubes from these, i.e.: 



1 L.B.B. = Lactose bile-salt broth. For composition see p. 180. 



