In autumn and early winter certain ditches around Cambridge became offensive, and their water turned milky. This led to a grave suspicion of sewage contamination, which, however, was satisfactorily disproved. On the other hand certain bacilli with single flagella were isolated from the water of the ditches and found capable of giving off from their artificial cultures an odour comparable to that of the ditches. And to these bacilli, acting on the dead leaves which found their way into the water, and, probably, in conjunction with other anaerobic bacteria which were generating hydrogen disulphide, the sewage-like odour is attributed.

Certain patchy changes of colour in the leaves and wood immersed in the water are attributed to a chromogenic flagellate which was found growing on them.