SEWAGE AND SEWAGE DISPOSAL. 243 



Another organism which is potentially pathogenic, and very 

 common in sewage, is Bac. enteritidis sporogenes. This is credited 

 with being the cause of the autumnal diarrhoea of children and the 

 "English cholera" of adults. It is widely distributed, and occurs in 

 normal and typhoid excreta, so it is always well represented in sewage; 

 it is anaerobic in its mode of life, and the rods measure 1'6-4'8/x. in 

 length and 0'8 /u in breadth. Further, the individuals are motile and 

 normally form spores, which are large, oval, and situated near one of 

 the ends of the cell (Fig. 129). The growth of the 

 species in gelatine and in agar is attended by gas 

 production, and in the former liquefaction also 

 takes place. It likewise grows well in milk, pro- 

 ducing what is known as the "enteritidis change" : 

 after 36 hours of anaerobic incubation in milk at 37 C., the cream 

 is dissociated by the development of gas, so that the surface of the 

 medium is covered with stringy pinkish-white masses of coagulated 

 casein, enclosing a number of gas bubbles. On the average there 

 are about 100 spores of Bac. enteritidis sporogenes in one c.c. of 

 normal sewage, but being in the spore condition the species can 

 be easily isolated by boiling the sewage sample for a couple of 

 minutes before making the usual plate cultures : the boiling kills all 

 the bacteria that are not in the spore condition, thus greatly increasing 

 the chances of the appearance of this species on the plates. The ease 

 with which this species can be isolated, its well-marked morphological 

 characteristics, especially in the sporogenous condition, and its 

 abundance in sewage, have all combined to make this organism valuable 

 to the sewage expert, as one of his chief bacteriological means of 

 detecting sewage contamination. 



Another class of closely-allied organisms found normally in sewage, 

 sometimes in very large numbers, is the Proteus group, mention of 

 which has already been made in dealing with the work of the 

 saprophytic bacteria. The group -includes Proteus vulgaris, P. mira- 

 bilis, P. Zenkeri, and P. cloacinus. They must be treated here in 

 greater detail, because they thrive well in sewage, and there may be as 

 many as 1,000,000 individuals of one or more members of the group in 

 one c.c. of sewage. As a class the members may be distinguished by 

 the following characteristics : They are motile ; they liquefy gelatine ; 

 they produce gas in glucose and sucrose, but not in lactose media ; they 

 curdle and acidulate milk, but very slowly ; they produce indol ; they 

 do not form endospores ; they are strongly aerobic ; and, when grown 

 in albuminous media, cause the formation of foul-smelling products. 



