62 



One of the great difficulties in the preparation of Endo medium is 

 the adjustment of the reaction. In most of the methods the reaction is 

 adjusted on the phenol phthalein scale to some definite point and then a 

 quantity of sodium carbonate is added to make it more alkaline. This 

 is a rather inaccurate method and results in some batches being very ser- 

 viceable while others are almost worthless. 



Levine suggested a modified and simplified Endo medium which re- 

 quires no adjustment of reaction and which need not be filtered. The 

 medium consists of 1 percent Difco peptone, 0.3 percent dipotassium phos- 

 phate, 0.5 percent agar, and 1 percent lactose. One-half c. c. of a satur- 

 ated basic fuchsin, decolorized by 2.5 c. c. of a 10 percent sodium sulphite, 

 as recommended by the Hygienic Laboratory, is employed as an indicator 

 for each 100 c. c. of the medium. Aside from the simplicity of prepar- 

 ation, an advantage claimed is that Bact. coli may be differentiated from 

 Bact. aerogenes. The former possess a distinct metallic sheen, the colonies 

 are flat and button-like, and about two or three m. m. in diameter; whereas 

 the latter usually produces considerably larger colonies which are convex 

 and a metallic sheen is rarely observed. The disadvantage of the medium 

 is that diffusion of color, due to acid production, is very rapid. This 

 may be reduced by increasing the content of agar but when that is done 

 the differentiation between Bact. coli and Bact. aerogenes becomes less dis- 

 tinct. 



All of the Endo mediums above have the disadvantage of instability. 

 Exposure to light or air induces a deep red coloration which interferes 

 seriously with the detection of acid formers thus making it necessary to 

 prepare the medium fresh and at frequent intervals. 



Kahn suggests the use of Endo medium in tubes instead of plates 

 inoculating from the presumtive test onto the slant and also into the butt 

 in a manner analagous to the Russel double sugar medium. He states that 

 Endo agar prepared and sterilized in tubes may be kept from three to four 

 weeks without deterioration and that anaerobes will not develop in the 

 butt of the Endo agar tube. Thus the test for acid production under aero- 

 bic and gas formation under anaerobic conditions by members of the colon 

 group is determined simultaneously thereby performing both partially 

 confirmed and a complete test, described above in a single tube. This 

 use of the Endo medium is very interesting and suggestive and worth trial 

 and consideration. 



The Eosin Methylene Blue Agar Confirmatory Medium. Le- 

 vine, in 1917, suggested a modification of the eosin-methylene blue agar 

 (first described by Holt, Harris and Teague) for the confirmation of the 

 presumptive test. The medium is prepared in the following manner: 



Distilled water 1000 c. c. 



Peptone (Difco) 10 gm. 



Dipotassium phosphate 2 gm. 



Agar 15 gm. 



