GENERAL CONSIDERATIONS 15 



Our knowledge as to the distribution and viability of the 

 different varieties of streptococci is very incomplete. 



As regards the distribution of B. enteritidis sporogenes under 

 saprophytic surroundings the investigations made have usually 

 not accurately differentiated this organism from very closely 

 allied forms, and the results which have been obtained for 

 the most part refer to the distribution of the spores of the 

 organisms which cause the so-called "enteritidis change" in 

 milk. This change is, however, usually due to B. enteritidis 

 sporogenes, and for practical purposes the results obtained may 

 be taken as showing the distribution of this bacillus. 



The spores of this bacillus are present in soil and, while 

 they are more abundant in polluted than in virgin soils, they 

 are present to some extent in soils not recently contaminated 

 (see Chapter IV). 



Klein and Houston found virulent B. enteritidis sporogenes 

 spores present in most of the samples of grain (wheat, oats, 

 rice, oatmeal and wheat-flour) examined. One gramme had 

 usually to be examined before positive results were obtained. 

 Balfour Stewart also found the spor.es prevalent in grain. 



In considering the value of this organism as an excretal 

 indicator, it must be remembered that it is a spore-bearing 

 bacillus and that its spores are very resistant. Animal ex- 

 cretal pollution is so widespread that it is not a matter of 

 surprise that such a highly resistant organism should be widely 

 distributed in nature. The available evidence shows that it is 

 absent, or relatively absent, from sources which have never been 

 contaminated, but that it is fairly prevalent in sources the pollu- 

 tion of which had taken place possibly at a long antecedent 

 period. These considerations obviously place a considerable 

 limit to its usefulness. 



The other conditions of suitable bacterial indicators refer to 

 the readiness with which they can be isolated, estimated and 

 accurately defined. All three groups, although they possess 

 drawbacks, fulfil these conditions. From this point of view 

 the streptococci are the least satisfactory, and really satisfac- 

 tory methods for their isolation and differentiation are greatly 

 needed. Thanks to the numerous investigations which have 



