Summary.1Experiments made to discover the death‐point of protozoa by phenol, carbon bisulphide and heat showed that phenol has a greater lethal effect than carbon bisulphide.2Heating the soil in a steamer for thirty minutes is usually sufficient to kill off the protozoa, and the treatment of glass‐house soil by steam destroys the majority of the protozoa and has a depressing effect on their numbers for a long per