<qa>  What is the model that allows for a stable bacterial population to be established before addition of2. a three compartment model with continuous flow of media, test compounds and bacteria from the entrance port of the first chamber to the exit of the third chamber mimicking movement through the three main compartments of the colon. This model allows for a stable bacterial population to be established before addition of test compounds, and can remain viable for up to 40 days. In the case of these longer incubations, multiple time points can allow for quite complex experiments looking at interactions between bacteria, food and pharmaceutical products where different factors are added at different time points. 