On the numerical distribution of micro-organisms in the atmosphere

Abstract

In 1887, Frankland (1887) devised a method for the quantitative estimation of the micro-organisms present in the atmosphere and experimented also (Frankland and Hart 1887) with a method described by Hesse. Frankland published a curve showing the seasonal variation in the number of micro-organisms in the air of London. Saito, in 1904, using the plate method, carried out a series of experiments at Tokyo throughout a whole year with the object of studying seasonal variation. In 1910, Buller and Lowe, using both the plate method and Frankland’s quantitative method, investigated the seasonal variation in the number of micro-organisms in the air of Winnipeg. Preliminary observations made by the present author in this country in 1929, showed that the number of micro-organisms falling on plates in a given time vary very greatly with locality. Extreme values were recorded (Horne, 1930, p. 164) for sea-level at Sligachan, Isle of Skye (1 per 100 sq cm per min) and for an orchard at Exning, Cambridgeshire (176 per 100 sq cm per min). It was also observed that the numbers varied with situation in a given locality even when the distance between the centres compared was not very great. It was impossible to discover from the literature on the subject whether any significance could be attached to the observed differences since none of the earlier investigators had a sound statistical method at their disposal. The work of Fisher (1930) has supplied this need. It was decided therefore to work more systematically in order to discover what principles, if any, govern the distribution of micro-organisms in the air. If the type of distribution could be established, then it should be possible to interpret the experimental results with the aid of methods of statistical analysis.