ABSTRACT
The interrelationships that exist between various groups of Protozoa in nature and the bacteria which occur in the same environments are undoubtedly of more than academic interest. This is especially the case perhaps in soil, where both types of organisms are present in very large numbers, and where a marked degree of activity is evidenced by the continual fluctuation to which these numbers are subject. The food relationships of one member of the soil population, the amoeba Hartmanella hyalina, was described in a previous paper (2), where it was shown that certain kinds of bacteria afforded a more efficient food supply than others as judged by the reproductive rate of the amoeba. A priori this might have been due to the fact that the bacteria giving a high reproductive rate to the amoebae were of greater food value than the others ; or that the by-products formed by the less valuable bacterium in the course of growth were deleterious in their effects; but preliminary experiments indicated that for the species of bacteria concerned it was a true food value effect and not one caused by the presence of any by-products.
In an earlier paper (2) this was stated to be impossible; experiments in that case were carried out on nutrient agar.
