146 EXCREMENTAL ORGANISMS 



has yet to be determined but the present trend of opinion is 

 towards the view that the methyl red negative, Voges and 

 Proskauer positive types (grain types) are harmless sapro- 

 phytes. The members of the B. coli group derived from human 

 and bovine hosts can be partially distinguished by the usual 

 reactions in sugar broths, the proteoclastic cleavage of gelatine, 

 and the production of indol from peptone, but these reactions 

 are not sufficiently specific for routine work although they have 

 a limited application for research purposes. 



2. B. Enteritidis Sporogenes. As the spores of B. enteri- 

 tidis sporogenes are present in considerable quantities in 

 manure and do not multiply in milk, the estimation of these 

 would constitute an admirable test for original pollution if all 

 other sources of these spores could be eliminated. The spores, 

 however, may be derived from dirty vessels and in practice it 

 is found that milk cans form a most fruitful source of these 

 organisms. Milk cans, unless thoroughly sterilised with live 

 steam, are very liable to contain large numbers of spores of 

 various organisms as the treatment given, though usually 

 sufficiently severe to kill the non-sporulating organisms, is not 

 drastic enough to kill the spores. The usual temperature at 

 which milk is pasteurised (143-145 F.) is also not sufficiently 

 high to kill the spores, so that the spore test is of considerable 

 value in arriving at an opinion as to the bacteriological condi- 

 tion of pasteurised milk previous to pasteurisation. This test 

 is, however, of much smaller value than the direct microscopical 

 test previously described. 



For the estimation of B. enteritidis sporogenes spores, 

 various quantities of the milk are measured out into sterile 

 test tubes, heated in a water bath at 80 C. for fifteen minutes, 

 cooled, and incubated anserobically at 37 C. To obtain 

 anaerobic conditions the tubes may be placed in an air-tight jar 

 containing alkaline pyrogallic, but satisfactory results may 

 be obtained by covering the surface of the sample in each tube 

 with paraffine; it is rather doubtful whether even this precau- 

 tion is necessary, as the butter fat which rapidly rises and seals 



