III. Some notes on soil protozoa

Abstract

It is rather a curious fact that it has been left to agricultural chemists to bring into prominence the important part that free-living Protozoa may play in the soil. At the present time it seems to us that the prevalent idea as regards the distribution of free-living protozoa is that they can exist in the trophic state only in definite accumulations of fresh water ( e. g ., pools, rivers, lakes) or in the sea. It seems also to be generally held that after the drying up of small pools the cysts of protozoa are transported by currents of air, and that it is to these wind-borne cysts that the prevalence of protozoa in cultures of ordinary soils may be mostly attributed. It is very difficult to trace the historical origin of this view, but it is evident that to the early workers on protozoa the idea of this limitation of their active life to water was unthought of. It is unnecessary to refer here to the works of very early writers, by whom the spread of disease was sometimes attributed to invisible forms of life present in the air. It would seem, however, from the following quotation that Ehrenberg held a far wider view as regards the distribution of protozoa than that which is fashionable at present. In his great work ‘Die Infusionsthierchen als Yollkommene Organismen,' p. 496, he says:—