A method of estimating the numbers of soil Protozoa, especially amoebae, based on their differential feeding on bacteria

Cultural methods of estimating protozoal numbers in soil based on a dilution technique have suffered from two main sources of error: first, the use of too few replicate cultures and, secondly, the uncertain quality of the bacterial food supply. A method is described of using glass cells to set up 8 replicate cultures in one Petri dish, employing pure bacterial cultures spread over a non‐nutrient agar base to provide a standard and suitable food for the Protozoa. The selection and testing of suitable bacterial strains as food supply is described. Tests for the ‘recovery’ of counted suspensions of Protozoa added to sterilized soil were made; the results of these are given and the limits of experimental error in the method are discussed.