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BACTERIAL TREATMENT OF SEWAGE 



sewage, we may attempt a provisional list of normal types of sewage 

 bacteria* as follows: — 



1. Bacillvs coli communis and all its varieties and allies. Houston 

 reports as many as 600,000 B. coli per c.e. in London sewage.' 



2. The Proteus family ■ — Proteus mdgaris, P. Zenkeri, P. mirahilis, 

 and P. cloacinus, first isolated from putrid meat by Hauser, isolated 

 from sewage by Jordan, etc. Houston also reports that frequently 

 there may be 100,000 "sewage proteus" present in one c.e. This is 

 an aerobic, non-chromogenic, actively motile, and rapidly liquefying 

 bacillus with round ends, one flagellum, and no spore formation. It 

 differs in essential particulars from the P. vulgaris. Some of the 

 cultures were pathogenic to guinea-pigs (Plate 14). 



3. Bacillus enteritidis sporogenes of Klein. The number of spores 

 of this organism found in London sewage by Houston varied from 

 10 to 1000 per c.e, thus often exceeding in number the total number 

 of spores of aerobic bacilli. The relative numbers of B. coli and the 

 spores of B. enteritidis sporogenes in crude sewage have been demon- 

 strated by Klein and Houston in the following table : — 



* The methods adopted for making a quantitative and qualitative examination 

 of sewage are precisely analogous to those used in milk research. Dilution with 

 sterilised water previous to plating out on gelatine in Petri dishes is essential (1 c.e. 

 to 10,000 c.e. of sterile water, or some equally considerable dilution), otherwise the 

 large number of germs would rapidly liquefy and destroy the film. The plate 

 should be incubated at a definite temperature, which is usually 20° C. Special 

 methods must be used for the isolation of special organisms, phenol-gelatine ( '1 c. c. 

 of a 5 per cent, solution of phenol to every 10 c.e. of gelatine). Eisner medium, 

 Parietti broth, indol-reaction, and "shake" cultures in gelatine (for testing gas- 

 production) must often be restored to for certain species. Spores in sewage may 

 be isolated by adding 1 c.e. of diluted sewage (1-10) to 10 c.e. of melted gelatine in 

 a test-tube, and heating the mixture to 80° C. for ten minutes before pouring out 

 Into the Petri dish. This temperature kills all the bacilli, but leaves the spores 

 untouched. The same plan is adopted in principle for separating B. enteritidis 

 sporogenes : a small quantity of sewage is added to 15 c.e. of fresh sterile milk, which 

 is heated at 80° C. for ten minutes, and then incubated at 37° C. anaerobically in a 

 Buchner tube. B. coli communis is grown in phenol-broth for twenty-four hours, 

 and then plated out on phenol-gelatine. 



