GENERAL CONSIDERATIONS II 



never show the smooth unseptate filaments characteristic of 

 the bacillus of malignant cedema. If cultures of diminished 

 virulence are used the pathogenic effects are somewhat modified. 

 The virulence of this organism is subject to considerable varia- 

 tion, to some extent dependent upon its source. 



The changes in milk cultures and the demonstration of the 

 pathogenicity of the whey, along with the post-mortem appear- 

 ances described, are quite sufficient for the identification of this 

 organism. 



Since B. butyricus and the other culturally nearly identical 

 organisms have a very similar distribution in Nature, it is not 

 usually considered necessary to carry out the pathogenicity 

 test in every instance. The diagnosis is then based upon the 

 characteristic "enteritidis change" in the milk. 



Bacterial indicators of excretal and sewage^utamination. 



These three groups B. colt, streptococci ^B B. enteritidis 

 sporogenes are very extensively employed to estimate the extent 

 of excretal or sewage contamination and it is of great importance 

 to consider critically the value of these determinations for this 

 purpose. 



The conditions of a perfect bacterial indicator are fairly- 

 definite and obvious. They are : 



1. It should be abundant in the substances, for which its 

 presence serves as an indicator. 



2. It should be absent, or at least relatively absent, from all 

 other sources. 



3. It should be easily isolated and numerically estimated. 



4. Its characteristics should be definite and not liable to 

 variation, whereby its distinctive characters might be impaired. 



All three groups are extremely abundant in both human 

 and animal excreta and in sewage. 



As regards human excreta B. coli group organisms are 

 present to the extent of 100 million to 1000 million or more 

 per gramme, streptococci are usually equally numerous, while 

 about I million to 10 million B. enteritidis sporogenes are present 

 per gramme. 



