Citric Acid Production by Aspergillus Niger*

the Stokes' equation (4). The anomalous appearance of the curves might suggest that a non-random sample had been selected, but examination of the frequencies of cells appearing in different size ranges reveals a normal distribution indicating that a random sample had been selected. The diameters of cells and the correspondent frequencies are: 3.5-2; 4.0-7; 4.5-10; 5.0-20; 5.5-17; 6.0-8; 6.5-2; and 7.0-1. Correlation studies revealed a high degree of correlation between volumes and weights, indicating a high degree of accuracy of the observations. The weight of each cell was calculated by multiplying its volume by its density as determined independently by experiment. Had all individual volumes been multiplied by the average density, then correlation would automatically be complete, but since densities of individual cells were calculated by a series of independent and unrelated observations and measurements, a coefficient of correlation approaching 1 is indicative of the accuracy of the different measuremen.ts. Spot diagrams of weights and densities and of volumes and densities did not reveal a high degree of correlation, although there is some indication that the larger, and hence heavier, cells are less dense than the smaller, lighter cells.