360 PUBLIC HEALTH BACTERIOLOGY 



streptococci isolated, 15 per cent were of the lamirasacsal 

 variety, whereas in cow-dung 58 per cent of those isolated 

 were of this variety. 



Houston gives thus his chief reasons for considering the 

 streptococcus test of value in the examination of water 

 supplies : 



1. That streptococci are superabundant in human 

 faeces. 



2. That faecal streptococci are absent or non-discover- 

 able in a relatively large volume of pure water. 



3. That faecal streptococci do not multiply in pure water. 



4. That some faecal streptococci are of feeble vitality, 

 and that the presence of such in a water, if they could be 

 differentiated from their more robust companions, would 

 seem to indicate pollution of recent and therefore of a 

 specially dangerous nature. Dr. Houston concludes that 

 human faeces usually contain a multitude of streptococci, 

 100,000 per gramme being an underestimate of the average 

 number. 



V. Bac. Enteritidis Sporogenes. Inoculate 10 c.c. of 

 sample water into 10 c.c. " whole " sterile milk. Heat to 

 80 to 85 C. for ten minutes. Cool in running water, and 

 incubate anaerobicallyin aBuchner's tube at 37 C. for forty- 

 eight hours. Examine for coagulation. The curd is almost 

 completely separated from the whey, and is torn by gas 

 formation, part gathering with the cream at the top. The 

 whey is only slightly turbid, and contains numerous bacilli. 

 The growth has the odour of butyric acid, and the B. 

 enteritidis sporogenes is distinguished from the B. butyricus 

 of Botkin only by its pathogenicity when injected into a 

 guinea-pig, which dies twenty-four hours after, with green 

 discoloration and oedema at the seat of entry, and there 

 may be gas formation, gangrene, and a disagreeable odour. 



VI. Isolation of B. Typhosus. This is a very difficult 

 procedure for various reasons. The most important are : 

 The small numbers of B. typhosus usually present ; their 

 rapid disappearance from sewage-polluted water, so that 

 they are often absent when fresh cases arising from a 

 polluted water occur that is, they die out in about the 

 same time as the incubation period of the disease ; and the 



