The changes produced by the growth of bacteria in the molecular concentration and electrical conductivity of culture media / by G.N. Stewart.

  • Stewart, G. N. (George Neil), 1860-1930.
Date:
[1899?]
Catalogue details

Licence: Public Domain Mark

Credit: The changes produced by the growth of bacteria in the molecular concentration and electrical conductivity of culture media / by G.N. Stewart. Source: Wellcome Collection.

    4/22 (page 236)
    ities. In this case the electrical conductivity can he taken as directly proportional to the total concentration of the electrolytes. If more than one electrolyte is present and the ionic velocities are Avidely different, then a quantitative determination of one or more of the electrolytes may be made by chemical methods, and the concentration of those that remain be deduced from the electrical conductivity. And even in complex solutions, when without actually knowing the ionic velocities we know the limits between which they must lie, we can often determine from the electrical conductivity whether the number of dissociated molecules in a given volume is increasing or diminishing, and, within certain limits of accuracy, by how much it is increasing or diminishing. This calculation can be controlled and the limits of error narrowed by taking account of the total molecular concentration (including that of the dissociated ions) deduced from observations on the freezing point. Tor instance, if we found that certain bacteria growing in solution of albumin caused a diminution in the freezing point without any change in the electrical conduc¬ tivity, this would indicate that the large albumin molecules were being broken down into smaller, but as yet non-dissociable, molecules, possibly into peptones. If, later on, we found that while the molec¬ ular concentration, as indicated by the lowering of the freezing point, was still increasing, the electrical conductivity also began to increase, we should have to conclude that in the course of the decomposition the point had now been reached where some of the comparatively small molecules were at length dissociable. If the molecular concentration and the electrical conductivity were found both to increase from the beginning of the bacterial growth, it would be proved that the decom¬ position even at the beginning went as far as the production of the dissociable electrolytic molecules. With the view of obtaining some nreliminary notion of the magni¬ tude of the changes which were to be expected, I made a series of experiments on the growth of ordinary putrefactive bacteria in blood and serum, and of pure cultures of certain bacteria in solutions of Witte’s “ peptone.” The freezing-point determinations were made by means of a modification of Beckmann’s apparatus, and the electrical resistance was measured by the telephone method of Kohlrausch. It