SOIL AND SEWAGE 65 



soil with crude sewage and studied the fate of certain sewage 

 organisms B. coli, streptococci, and B. enteritidis sporogenes-^- 

 in the treated soil. While all these organisms were abundantly 

 present in the soils immediately after inoculation, all diminished 

 with time, although their rate of disappearance varied greatly. 

 The majority of the streptococci very rapidly disappeared, the 

 B. coli less rapidly, and showed considerable variability, while the 

 spores of B. enteritidis sporogenes showed but slight diminution 

 during the period of observation. 



Some experiments of the writer 1 upon the self-purification of 

 tipped house and street refuse constituting "made soil," illustrate 

 the gradual replacement of the B. coli and other organisms, 

 originally present abundantly in the tipped refuse, by B. mycoides 

 and other soil organisms. In these experiments "made soil" 

 (the samples being collected at a depth of 2 feet) was examined, 

 taken from deposits of known ages. In the samples deposited 

 within two years B. coli group organisms were abundant, while 

 the numbers of B. mycoides and cladothrix were either very few, 

 or these organisms were absent altogether. Jn material deposited 

 several years previously, on the other hand, no B. coli were 

 found, while the soil organisms mentioned were very numerous. 

 The soil organisms had replaced those in the original material. 

 There was a general relationship between the number of B. coli 

 and the age since deposit. 



The same facts are brought out from the results of the 

 examination of soils from different sources for these sewage and 

 excretal bacteria. Houston, Chick, Savage and others have 

 examined soils for these organisms. In virgin soils typical 

 B. coli and streptococci are absent, while spores of B. enteritidis 

 sporogenes are either absent, or present in only very small 

 numbers. On the other hand, in cultivated and other con- 

 taminated soils all these organisms are present in numbers 

 roughly comparable to the extent and age of the contamination. 



The following results obtained by the writer 2 will serve as 

 an illustration of findings likely to be obtained. 



1 Journal of Sanitary Institute, 1903, vol. XXIV, p. 442. 



2 The Bacteriological Examination of Water-Stipplies. H. K. Lewis, London, 

 1906. 



S. W. c 



