A statistical study of the form and growth of a spore-bearing bacillus

Abstract

The rate of growth of Bacillus megatherium has been measured by direct counting of the cells, using a haemocytometer; and the average length of the cells has been determined by measurements made at the same time. In agar cultures inoculated from a 12-hour agar culture (which has nearly reached the maximum of growth but has not yet formed spores) it was found that the cells began to increase in size during the lag phase and reached a maximum length, about six times that of the inoculated cells, shortly after the beginning of the maximum growth phase, then rapidly becoming shorter. During the period of increase in length, frequency curves showed a tendency towards bimodality, indicating that possibly a process of selection of rapidly growing cells may occur during the lag phase, as has been suggested by some investigators.

Two series of broth cultures inoculated from a 7-hour agar culture (during the period of maximum growth) showed no lag phase; nevertheless an increase in the size of the cells was observed beginning two hours after inoculation.

Two series of broth cultures inoculated from a 7-hour agar culture (during the period of maximum growth) showed no lag phase; nevertheless an increase in the size of the cells was observed beginning two hours after inoculation. The cells did not become so large as did those on agar, and the variation was not so great, bimodality being present in but one of the frequency curves. One series was inoculated with 10 times as many bacteria as the other, and the series receiving the lesser amount of inoculum showed a slightly greater increase in the size of the cells over a slightly longer period of time.