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.

    5/22 (page 237)
    will be seen from the subjoined specimens of the results that very striking changes are observed both in the total molecular concentration and in the electrical conductivity, which, upon the whole, run a par¬ allel course. Thus, in Experiment I, dog’s defibrinated blood and serum were allowed to putrefy for 6 weeks in a bath at a temperature of 37° to 39° C. The electrical conductivity of the blood in that «y time was increased more than eleven-fold, and the freezing point was depressed in proportion. There was a similar change in the serum, although the maximum was much less. Curves plotted from the results of this experiment are shown in Plate V. In Experiment II, three specimens of blood taken at the same time from the carotid artery of a dog were allowed to putrefy first at the air temperature, then at 35° C., and then at 40° to 43° C. Of course in all the experiments evaporation was prevented. The course of the decomposition is shown in the curves of Plate VI, which represent the electrical conductivity. It is abruptly hastened by raising the tem¬ perature to 35° C. Ultimately the conductivity reaches a maximum and then remains practically constant for an indefinite period. At the time when the maximum was reached the blood was seen to be crowded with bacteria which had formed spores. It is to be pre¬ sumed that at this point the conditions had become unfavorable for the growth of the bacteria, owing to the increase of osmotic pressure due to the accumulation of the products of their activity or to some specific toxic action of these products and the using up of the nutritive material. A specimen of the blood at this stage was diluted with its own volume of water so as to diminish the concentration of the waste- products, and a renewed period of growth, indicated by a steadily mounting electrical conductivity, was again observed. It may seem strange that bacteria should be able to grow at all in a liquid whose osmotic pressure is 8 or 10 times as great as that of normal blood- serum or the cell-sap of ordinary vegetable cells. But Wladimirofi * has shown that the osmotic pressure in the interior of bacteria is ex¬ traordinarily great, more than 3 times that of the cells of the higher animals. And if the bacterial cell-wall is freely permeable to any of * Zeitsch. f. physikalische Chemie, vii, 529.