1S6 



ROYAL SOCIETY OF CANADA 



Experiment 2.~ A Petri dish witli aesculin medium containing 0.2% of iron citrate, 

 acidity + 0.2, with colonies of B. ccli. 



II.-The dark shaded portion represents the darkening or blackening of the 

 field, due to the diffusion of the hydrochloric acid, that has dissolved again the iron 

 citrate. 



