Investigations into a Method for Counting the Total Number of Bacteria in a Suspension

Summary: Counts were made of the total number of bacteria in cultures by a method that comprised suspension of the cells in molten agar, and the casting of this agar into a thin film in a haemocytometer chamber, followed by removal of the film from the chamber and drying in air. Counting of the bacteria was carried out with the use of a phase-contrast microscope. Statistical analysis of the counts indicated that the principal sources of variation lay in the differences between the numbers of organisms counted in successive microscope fields, between the total numbers in different traverses of the film, and between the primary agar dilutions of the culture.