Year 6 were keen to check out whether some of the medieval cures for the plague (about which they had learned) might actually have made some difference to the health of the unfortunate victims.
Clearly, infecting each other with deadly diseases for the advancement of scientific knowledge falls well outside the remit of the National Curriculum and the boundaries of common decency. Therefore, as an alternative, the children used slices of white bread, which they generously annointed with various substances (e.g. milk, figs, onions, rose-water etc.) and then left for several days (sealed in plastic bags for reasons of health and safety) so that they could observe the progress of any microbial life which might develop on each.
Some of the susbstances (e.g. rose water) did indeed seem to inhibit the growth of micro-organisms on the bread. This might mean that these substances could have had a similar impact on the plague bacterium - but clearly, further testing would be required to confirm this.
As Mrs T said to her students, scientific experiments often raise as many new questions as they answer - and this is exactly how our knowledge progresses...