106 BACTERIOLOGICAL EXAMINATION OF WATER. 



B. coli affords a much more delicate test of pollution than any 

 chemical examination which can be made. Experiments have 

 shown me that when pure water is polluted with a highly 

 concentrated sewage the limit of the dilution in which the 

 contamination can be detected chemically is 1 in 1000. Dilutions 

 of 1 in 10,000 and 1 in 100,000 showed no chemical signs of 

 pollution ; but when examinations were made for B. coli, this 

 organism was detected with the greatest ease in 1 c.c. of the 

 1 in 100,000 dilution. 



Klein and Houston examined eight samples of sewage obtained 

 from different sources in various dilutions. They found that, 

 as a rule, a dilution of 1 in 1000 could be detected chemically, 

 but the dilutions of 1 in 10,000 and 1 in 100,000 gave no 

 chemical indication of pollution ; but in all the dilutions the 

 presence of B. coli was usually demonstrated directly without 

 resorting to the " filter brushing method." 



The statement of Levy and Bruns that B. coli from stools 

 are pathogenic, whereas those found in pure waters are not, 

 has been re-investigated by Weissenfeld. Blachstein, in 

 1893, pointed out that if a tube of broth be inoculated with 

 1 c.c. of good drinking water and incubated at 30 C. for 

 forty-eight hours, 2 c.c. of the mixture can be injected 

 intra-venously into a rabbit or intra-peritoneally into a guinea- 

 pig without inconvenience to either animal. If, however, the 

 water be from a contaminated source, such as the Seine, both 

 animals, as a rule, rapidly succumb. The lethal effects of the 

 impure water were attributed to the B. coli and its varieties. 

 Sims Woodhead and Cartwright Wood injected guinea-pigs 

 subcutaneously instead of intra-peritoneally, and took the 

 presence or absence of local reaction as the test of contamination 

 or purity because they found it was quite the exception for 

 water supplies in England to be so contaminated as to exert a 

 lethal action. Even when the organisms present in tap-water 

 were allowed to grow for weeks in broth and so heap up their 

 products, they produced practically no effect. 



Weissenfeld's experiments were made either with pure broth 

 cultures of the B. coli, which he isolated from the wells 

 before mentioned, or else with a mixture of the waters and 

 broth cultures as in Blachstein^s experiments ; 1 c.c. of a 



