Current Intensity Factor in Electrocution of Paramaecia

Abstract

The purpose of the present work is to determine in absolute values the intensity of current required to pass through a Paramaecium to disrupt it. The organism, Paramaecium caudatum, cultured for 5 to 6 days in hay infusion, which consisted of Timothy hay boiled for 5 minutes in 100 cc. of distilled water and diluted to 500 cc. was introduced into a glass tube of known diameter and length. The tube was placed horizontally on a disc of hard rubber, the ends being immersed in big drops of culture medium into which the electrodes carrying the current (D.C.) were also introduced. The disc, placed on the stage of the microscope, was hollowed in the middle so as to allow the light from the condensor to pass through. Rheostats and milli- or microammeters, in series, completed the circuit. When a paramaecium came in sight in the tube the circuit was closed and the data taken. Selecting only those experiments in which the organisms were disrupted instantaneously (in less than 1/5 of a second) a “Band of killing intensities”, extending from the intensities that killed about 5% to those that killed about 95%, was established for a set of tubes varying widely in diameter. The following results were obtained: (cross sectional area of the tubes less cross-sectional area of the organism, in mm2, in line A; band of killing intensities in microamperes, in line B). The average of the 2 extreme intensities of the “band”, plotted on the curve, (Fig. 1) show an evident linear relation. The system consisting of a paramaecium in suspension in its medium, in a thin glass tube through which a current is made to pass, can seemingly be compared to a system of 2 conductors in parallel, one being the organism and the other the column of liquid having the length of the paramaecium and surrounding it.