Abstract
The method used for estimating the vitality of tissues by measuring their electric resistance has been applied, in the present investigation, to a suspension of yeast heated gradually until all the cells were killed.
A suspension of 3 gm. of yeast (Fleischmann's yeast) in 3 gm. of a N/5 solution of NaCl, was heated from 15°C. to 93° and then cooled to 15° in an Ostwald's conductivity cell immersed in a water bath, and the electric resistance of the suspension was taken at each degree. The time between 2 readings was one minute. A microphone Hummer, working on a 6 volts battery, delivered the alternating current of 1000 cycles, used in the conductivity bridge. The suspension was stirred before each measurement by moving the electrodes up and down. Previous tests showed that the concentration N/5 did not affect the resistance of the cells to an appreciable amount.
The results, plotted on the curve (Fig. 1), show:
1. From 15° to 62° and from about 60° to 15° the resistance behaves like the resistance of a salt solution, and the curve coincides with the resistance curve of a salt solution of convenient concentration.
2. From 62° to 67° the resistance falls abruptly. This irreversible drop is probably due to the death of the majority of the cells.
3. From 67° to 93° and from 93° to about 60° the curve shows a resistance higher than would be expected from a salt solution; at about 60° it coincides again with the typical curve of such a solution. This phenomenon suggests that above 67° the few surviving cells are killed.
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