556 REUBEN L. KAHN 



When testing out the growth of a number of strains of B. 

 coll under these conditions, it was observed that while the col- 

 onies on the surface of the slant were typically metallic, the 

 organisms growing in the butt, although showing gas produc- 

 tion, did not always redden the medium during the first twenty- 

 four hours of incubation. This fact, however, was not found to 

 interfere with our intention of utilizing the Endo tube rather than 

 the plate for the confirmatory test for B. coli in water. When 

 waters sent to this laboratory for examination showed gas for- 

 mation in lactose broth fermentation tubes, straight wire inocu- 

 lations were made from these tubes, to Endo tubes, extending 

 the wire first into the butt, then spreading the tip of the wire 

 over the slant. Endo plates were also inoculated as a check. 

 The results were always constant. When colonies of B. coli 

 were present on the Endo plates, typical colonies were present 

 also on the slant, with gas production in the butt. Occasionally, 

 after a given period in the incubator, the colonies on the plate 

 would require further incubation, while those on the slant would 

 be sufficiently metallic to render the test complete. 



This constancy of results, combined with the saving of time 

 and material by this new procedure, led to the complete sub- 

 stitution of Endo agar slants for Endo plates in the confirmatory 

 test for B. coli. 



The following procedure also, has been employed as a con- 

 firmatory test for B. coli: A loop from the lactose fermentation 

 tube showing gas, is spread over the surface of an empty Petri 

 dish. A tube of Endo agar is now melted in a water bath, cooled 

 to 40°C. and poured over the surface of the dish. When the 

 Endo agar is congealed, a loop from the same fermentation tube 

 is smeared over the surface of the agar. After incubation, if 

 B. coli be present, typical colonies will appear on the surface 

 and red colonies with gas bubbles, below the surface of the agar. 

 Thus an aerobic growth and a practically anaerobic growth is 

 obtained in one test. 



However, no marked advantage is gained when employing 

 this procedure over the simple Endo tube method described 

 above. 



