LIMITING FACTORS IN THE LACTIC FERMENTATION

Abstract

In the normal course of the lactic fermentation the bacterial growth passes through four stages: the lag period, the period of rapid or logarithmic growth, the period in which there is little or no increase in numbers, and the final period in which fermenta-tior ceasesand the cells slowly die. Ti-a-dianges from the first to the second and from the second to tL... ird period are comparatively rapid and are accompanied by mo)hological and physiological changes in the cells. The transit n from the third to the fourth period is gradual. In the third period the cells may be in a quiescent condition ina which there is little or no multiplication, or the multiplication and death rate may be so nearly balanced that the number counted remains constant. Counts made by the plate method would be likely to give the impression that the latter is the case since only the living cells are counted. If direct microscopic counts are made and the population remains constant it must be assumed either that the --cells are quiescent or that they lose their ability to take stain very soon after death. In our work on this problem we used a microscopic count in order to avoid as far as possible the error introduced into the plate method by the tendency of the lactic streptococci to grow in pairs and chains. The very large numbers of cells with which it was necessary to work militated against accurate counts, and it was difficult to obtain a series of counts which would give a reasonably smooth curve. However, the constancy with which uniform counts were repeatedly secured under similar conditions indicated that 211