1911.] The Influence of Ionised Air on Bacteria. 283 



of the bacteria examined. On account of the use made by previous experi- 

 menters of B. anthracis, B. typhosus, and B. coli communis, these were used 

 in determining the best conditions of exposure. 



In fig. 7 (Plate 7) the organism is anthrax exposed for 20 minutes, 

 10 minutes' exposure failing to show any effect. The colonies in the 

 control are large and uniformly distributed. In the central (positive) 

 plate they are cleared opposite two points, the third has missed fire. In 

 the negative plate the cleared areas are somewhat larger and the colonies 

 fewer. In fig. 8 the exposure was for 30 minutes, and the influence 

 of time and of difference of sign of charge is now unmistakable. The 

 positive plate is well cleared, the negative contains one colony only, and at 

 a corner where the wind is least likely to have taken effect. In fig. 9 

 (Plate 8) with 50 minutes' exposure of a dense sowing the positive plate 

 shows little growth, and on the negative there is one colony. Many hours' 

 exposure are necessary to completely sterilise the plates with certainty in 

 this way. Kg. 10 is of Pneumococcus, 1 hour 10 minutes' exposure. From 

 a very dense sowing only about a dozen colonies developed on the positive 

 plate and a few rudimentary ones on the negative. 



In the case of B. pyocyaneus, exposed as in fig. 1, the negative plate was 

 entirely cleared in two and a-half hours, the positive about one-half. The 

 control showed a dense growth. This may be regarded as a sensitive 

 organism, though not to the same degree as B. asiaticce choleras, given later. 



Sarcina lutea, exposed for two and a-half hours, gave nearly as many 

 colonies on the positive plate as on the control, the negative having only a 

 few small ones. 



6. On account partly of the long time sometimes taken to produce a 

 distinctive difference, the arrangement was changed to that shown at fig. 2. 

 The first exposure of B. coli communis was for 18 hours. On examining 

 the dish it was found that the discharge had dried the jelly, forming two 

 shallow pits, the smaller caused by the positive discharge, the larger by 

 the negative. The angle of the positive cone was one-half that of the 

 negative. 



The B. coli communis series is given in fig. 11 (Plate 9), fig. 13 (Plate 10), 

 and fig. 18 (Plate 11), the exposures in Plate 9 being 1£, 4^, and 18 hours 

 respectively. A good deal is cleared in the first, all but a small patch 

 in the bottom corner of the second, and the third entirely so. Fig. 12 

 is of B. typhosus, the times of exposure being 1 hour, £ hour, and 2\ hours. 

 There is a trace of clearing in the ^-hour plate, none at the positive 

 in 1 hour, though a good deal at the negative, and in 2\ hours an almost 

 clear plate. 



