A statistical study of the form and growth of Bacterium coli.

Abstract

In previous studies 1 of the form and growth of bacteria, the length of the cells has been taken as a measurement of size because apparently the width did not vary nearly so much, and because the width could not be determined accurately with the technique used. In the present study which has had for its purpose the establishment of the normal variations in size and form of Bacterium coli when grown on standard beef extract agar, a somewhat different technique was used. Photomicrographs were made from slides prepared by the negative staining method of Benians, and the photographic negatives were again projected so that the final magnification was 30,000 diameters. The projected image was traced on paper and from these tracings the length and area were determined. The growth curve was obtained by counting the cells by a technique which has been previously published. 2

The results are shown in the accompanying graph. The diagrams of the cells have been traced from composite photographs of the tracings of the projected images and indicate roughly the average size and form of the cells at the various time periods. The rate of multiplication is indicated by the curve of the logarithm of the number of cells. Assuming that the cells are symmetrical about the axis, the area of the projected image divided by the length squared may serve as an index of variation in form, just as the weight-length index has been used for higher organisms.