The Influence of Ionised Air on Bacteria. 



281 



5 inches diameter and 10 inches long, with stoppered openings at the top, 

 were supported on ehonite and glass insulators. The discharging points, 

 three fine steel sewing needles, were attached to a copper wire passing 

 through the stopper to an electrostatic machine, one of the jars being 

 connected in this way to the positive terminal, the other to the negative. 

 The opposite pole in each case was connected by a wire entering through 

 a central hole in the base plate to a thin metal disc, upon which was placed 

 a Petrie dish containing agar sown upon the surface with an emulsion in 

 water of the organism to be exposed. The distance of the points from the 

 agar was in no case less than a centimetre. 



3-ig.l 3ig.2 

 Fig. 1. — Discharging points in separate vessels. . 

 Fig. 2. — Discharging points over the same plate. 



The glow at the points could just be seen in diffused daylight. The 

 photograph of fig. 3 (see at bottom of Plate 12), taken with the needles 

 illuminated by a Nernst projector lamp, shows the proportions of the group 

 and the volume of the negative glow in each case. Prom the photo- 

 micrograph (fig. 4) the negative glow starts as a regular cone, drawn here 

 to one side by the proximity of the positive pole, and the positive glow 

 (fig. 5) appears on the side of the needle, in this case sharpened by affile cut. 

 The former has a vertical angle of 135°, converging upon a point about 

 015 mm. outside of the surface of the needle. 



The radial length of the glow is 0-10 mm., and its volume about 

 90 cu. mm. The positive glow is irregular and extended over a larger 

 area on the needle than the negative, though the luminous volume is only 

 about one-half that of the latter. With the arrangement shown in fig. 2 

 the current was 4 - 4 micro-amperes in both the positive and negative leads. 

 At the negative pole the rate of ionisation, assumed to all take place in the 



Y 2 



