SIMPLIFIED CONFIEMATORY TEST FOR B. COLI 559 



Of late we have been employing Endo medium of 2 per cent 

 agar, with good results. The surface of the slant is, as a rule, 

 dry and there is no difficulty in obtaining isolated colonies. 



There also exists some difference of opinion as to the amount 

 of fuchsin to be employed in Endo medium for colon work. In 

 this laboratory, 0.2 per cent of a saturated alcoholic solution of 

 basic fuchsin in agar is employed for the isolation of 5. typhosus 

 from feces. This amount of fuchsin approaches that suggested 

 in the ' 'Standard Methods," and although sufficient for typhoid 

 work, is too weak for the detection of B. coli in water. Hassel- 

 tine (1917) comes to the same conclusion. 0.5 cc. and 0.4 cc. 

 of a saturated alcoholic solution of basic fuchsin per 100 cc. 

 of agar have been employed with good results. Our findings 

 would indicate that 0.4 per cent of fuchsin is sufficient for colon 

 work. 



The method of sterilization suggested by Robinson and 

 Rettger (1916) has been employed for this medium. Stock 

 quantities of 2 per cent agar, titrated to 0.2 to phenolphthalein 

 are kept on hand. Just before tubing, proper quantities of 

 sterile lactose, fuchsin, and fresh sodium sulfite are added to the 

 agar previously melted in the Arnold. The tubing is carried 

 out with care to prevent undue contamination. The tubes are 

 then placed in the hot autoclave and sterilized from five to seven 

 minutes at 10 pounds pressure. After sterilization, the tubes 

 are slanted and covered with a towel to keep out the light, after 

 which they are placed in the ice-box and are ready for use. 

 , Whether or not typically metallic colonies are produced on 

 Endo medium by organisms not related to the colon group has 

 been under investigation for some time. When glycerol or 

 glucose is substituted for lactose in Endo medium, other organ- 

 isms beside B. coli, produce red colonies with a metallic film. 

 When, however, regular Endo m-edium is employed with lactose 

 as the carbohydrate, no metallic colonies were observed except 

 by members of the colon group. 



Fifty Endo plates were exposed to air and were then incu- 

 bated; twenty-five plates at 37°C., and twenty-five plates at 

 room temperature. Observations were made every day for two 



