For confirming the presumptive test for B. coli the mediums most frequently employed are litmus lactose agar and fuchsin sulphite (Endo) agar. It is becoming more apparent that the coli-like forms may be divided into two groups which are closely correlated with the source. One group (B. coli) is characteristic of fecal origin; the other (B. aerogenes and B. cloacae) is rare in feces, but constitutes the prevailing coli-like form in the soil and on grains. The standard litmus lactose and Endo agar may be employed to a slight extent for the differentiation of B. coli and B. aerogenes, but the differences between these types on these mediums (particularly L.L.A.) are not very clear-cut nor distinct. Better results are obtained with a modified Endo agar described elsewhere. A very excellent differentiation between the B. coli and B. aerogenes types has been obtained on a modification of eosin-methylene blue agar first described by HoltHarris and Teague for the isolation of the typhoid group from feces. The medium is prepared in the following manner: