[HARRISON & VANDERLECK] .ESCUIJN BILE SALT MEDIA 



1S8 



That dissociated iron is necessary for the test is shown graphi- 

 cally by the following diagrams, which represent three practical 

 experiments. 



Experitnent Z— A Petri dish with œsculin medium containing 0.01% of iron citrate 

 acidity + 0.6, with colonies of B. coli. 



L— The dark shaded portion represents the darkening or blackening of the 

 field, due to the diffusion of the iron citrate. 



