204 MILK AND THE PUBLIC HEALTH chap. 

 Byre Milk Samples. 



In addition, a large number of fresh milk samples were 

 kept at 15 ' C. and 20°-21° C. for 24 hours, and the acidity 

 re-determined. The results obtained showed the rather 

 striking fact that in many instances there was no increase at 

 the end of 24 hours in the acidity of samples kept at 15° C, 

 and sometimes none at 20°-21" C. The number of bacteria 

 including the B. coli group of organisms increased enormously, 

 so that for these incubated samples, which may be considered 

 to represent ordinary vended samples, there was still less 

 relationship shown between bacterial content and acidity. 



The acidity determination cannot be considered of value 

 in relation to bacterial contamination, and it is only retained 

 here since it is still advocated by several authorities. 



To estimate the acidity, place 2 to 5 c.c. of milk in a narrow 



beaker or test tube, add • 5 c. c. of phenol-phthalein solution (in 5 



N 

 per cent alcohol), and run in -— caustic potash to the first 



appearance of pink. The titration should be done with a co)i- 

 trol tube or beaker containing milk by the side, and must be 

 carried out in the cold. If the milk is boiled to expel COj, 

 very irregular results will be obtained due to decomposition of 

 certain constituents of the milk. 



.Fokmalin-Methylene Blue Reduction Time 



Shardinger in 1902 found that a mixture of methylene 

 blue and formalin is decolorised by the action of milk. The 

 reaction is due to the presence of a ferment readily destroyed 

 by heat, and this test was proposed by him as a means of dis- 

 tinguishing between raw and heated milk. 



