644 LABORArORV HINTS 



mixiure is then plated out on lactose bile-salt-neutral-red agar, which 

 is incubated at 37° C. for forly-eight hours. 



At the end of that time fifteen to twenty colonies are found to be 

 present on the plate. Two colonies are in any case picked off, and eacii 

 single colony is inoculated into a tube containing a few drops of sterile 

 water. From these tubes further inoculations are made into broth, 

 glucose-peptone, and four different special sugars are incubated at 

 37° C. The inoculated broth ttibe is examined at the end of eighteen 

 hours for motility and the production of indol. 



The glucose-peptone is inoculated for forty-eight hours and at the 

 end of that time, if a strong growth is present, a few drops of a very 

 concentrated solution of caustic potash are added for the purpose of 

 finding if the \^oges-Proskauer reaction is given. If this is present 

 a bright ^range-red colour is produced. It may take twenty- 

 four hours before this colour is apparent. The four sugars that are 

 inoculated are saccharose, sulcite, adonit and inulin. 



In these a positive reaction is represented at the end of forty-eight 

 hours' incubation at 37° C\ by the production of acid and gas. It was 

 assumed that the same species of bacillus ahvays fermented the same 

 sugar. In connection with the indol test the paradimethyl benzol- 

 dehyde reaction was alwa'ys used, as it seems to be a very delicate and 

 reliable test. With regard to the \\)ges-Proskauer reaction consider- 

 able difference of opinion exists, but there can be but little doubt that 

 it appears a good test for the B. cloacae, B. lactis aerogenes, and 

 Oxytocus perniciosus group. 



The term B. coli was only applied to Escherich's organisms. 



Experiment (i). 



Sample taken from the Blue Nile, two metres from the bank. 



Local rainfall nil. River steadilv rising for three weeks. 



Temperature of water, 27° C. 



Total colonies on agar al 37° C. were 218 per c.c. 



F'iecal bacilli present in 01 c.c. 



Sporogenes test plus in 20 c.c. 



Experiment (2). 



Sample from same place. Local rainfall nil. River steadilv rising 

 for two months. Temperature of water, 24*5° C. 



Total colon}- count in agar at 37° C. was 700 per c.c. 



Faecal bacilli present in o"i per c.c. 



Sporogenes test plus in 20 c.c. 



Experiment (3). 



vSample from shallow well sittialed in a native vard about a quarter 

 of a mile from the Blue Xile. 



The water was at a depth of 19 metres from the surface. 



The water temperature was 30° C. 



