GENERAL CONSIDERATIONS 15 



100,000 per c.c., streptococci 1000 10,000 or more per c.c. and 

 spores of B. enteritidis sporogenes 100 to IOOO per c.c. 



The second condition is that these indicator organisms should 

 be absent or relatively absent from sources other than those for 

 which they are to serve as an index. A great deal of work has 

 been carried out upon the distribution of these organisms in 

 saprophytic surroundings and while the results are not in com- 

 plete accord the work done has established certain general facts 

 in favour of the use of these organisms (and more particularly 

 the B. coli group) as a satisfactory measure of excretal or sewage 

 contamination. 



Dealing first with B. coli in soil the general facts set out 

 in Chapter IV show that members of this group are only 

 present when the soil has been contaminated with excremen- 

 titious matters and that virgin soil and soil not manured are 

 free from these organisms. Further it has been shown that 

 these organisms gradually die out in soil. 



Members of the B. coli group have also been found to be present 

 on wheat, rye and other grain and a number of investigations in 

 this direction have been made. The results, considered broadly, 

 show that when the grain is carefully collected directly from the 

 fields no B. coli are present, but that if the examinations are 

 made after ordinary storage members of this group are frequently 

 found in small numbers. It is to be anticipated that stored 

 grain will often show B. coli on examination in view of the fact 

 that these organisms are abundant in the excreta of rats and 

 mice, animals generally numerous in grain ships and storage 

 places. 



In quite pure water, pure air, etc. B. coli group organisms do 

 not occur. 



Briefly stated, we have, in the B. coli group, organisms which 

 are extremely abundant in excreta and sewage, but which do 

 not occur in air, water, soil or other substances unless they have 

 been in contact with excrementitious matter, while they do not 

 multiply to any extent under ordinary natural conditions, outside 

 the animal body. 



As regards the saprophytic distribution of streptococci there 

 is no evidence that streptococci have any true home, under 



