THE EXAMINATION OT WATER 643 



Dealing with river water, B. coli was found present in o'5 to i cc. 

 of the water taken near the bank but only in 5 cc. taken from mid- 

 stream. 



In shallow well water B. pyocyaneus was found and dysentery was 

 observed to follow the use of this water. 



Deep well water was examined by Captain Archibald with the 

 following results : — 



(i) The colony count in i cc. 

 This was always carried out with agar plates as the heat prevented 

 the use of gelatin. The percentages of the various constituents of the 

 agar was the same throughout all the tests. The acidity was plus 10 

 to phenol-phthalein. One cc, o'5 cc, and 02 cc of the water 

 sample is taken and run into melted agar at a temperature of 41° C. 

 This was then placed out in Petri dishes, incubated at 37° C. for 

 forty-eight hours, and all colonies visible to the unaided eye counted. 



(2) Sporogenes Test. 



Twenty cc of the sample of water are pui into sterile milk con- 

 tained in tubes. The milk is then heated up to 80° C. for twenty 

 minutes, and a laxer of hot vaseline is run on to the surface of the milk 

 so as to render the latter anaerobic. The milk tubes are then incubated 

 at 37° C. for forty-eight hours. 



Evidence of the presence of the spores of B. enteritidis sporogenes 

 is shown by the clotting of the milk. 



(3) The test for the presence of the lactose-fermenting organisms 



and their subsequent isolation. 



Lactose bile-salt-neutral-red-broth is used and, as varying quantities 

 of \vater are inoculated into tubes containing this medium, the latter 

 is made up in single, double, and triple strength. 



One tube is inoculated with 20 cc of the water, two tubes with 

 10 cc, four tubes with 5 cc, five tubes with i cc, and five tubes with 

 o'oi cc All are incubated at 37° C, only tubes that give both acid 

 and gas being counted as having given the reaction. 



If only one tube in the first seven of these gives a reaction, then 

 faecal bacilli are present in 60 cc, and if three out of the five i cc 

 tubes gives a positive reaction, then fascal bacilli are considered to 

 be present in i cc The same applies, more or less, to the o'l cc 

 and the o'oi cc groups. The next step in the procedure is to isolate 

 the various f^cal organisms present; and in order to do this satis- 

 factorily, the tube containing 10 cc of water or more, that has given 

 a positive reaction in forty-eight hours, is taken. Of this, three to five 

 platinum loopfuls are removed and inoculated into 10 cc of sterile 

 water. The latter is then vigorously shaken, and one loopful of this 



