1906.] Action on Bacteria of Electrical Discharges. 63 



current through the emulsion was obtained with the first described arrange- 

 ment (a), all the crucial experiments detailed in this paper were carried out 

 with the kind of tube described, fresh distilled water being usually used for 

 making the emulsion. Before proceeding it will be as well to give the 

 reasons for our assumption that with this type of tube the current when 

 discharged on to the surface is subsequently conducted directly through the 

 fluid. 



(1) When using the type of tube described the visible direction of the 

 discharge is directly on to the surface of the fluid, and not towards the sides 

 of the tube, as frequently is the case when the other arrangements are used. 



(2) On raising the platinum wire which passes through the bottom of the 

 tube from the mercury in which it is usually immersed a brilliant discharge 

 breaks from its lower end. 



(3) If the wire which passes from the mercury in the beaker to the gas 

 pipe is removed for about half an inch from the pipe a brilliant discharge 

 across the gap breaks. 



(4) If tap water was used instead of distilled water, or even if distilled 

 water which had been allowed to stand exposed to the air for a few days was 

 used instead of freshly distilled water, a considerable portion of the current, 

 instead of passing by the direct path through the fluid, appeared to pass from 

 the edge of the platinum disc to the side of the test-tube, and thence through 

 the water in the containing-beaker to the earth wire ; whereas, when freshly 

 distilled water was used, there was no indication of discharge' towards the side 

 of the tube, but the discharged current appeared to impinge directly on to the 

 surface of the fluid, and apparently passed through it to the wire at the 

 bottom of the tube. 



(5) Unless special means were adopted for keeping the tube cool, a con- 

 siderable and rapid rise in the temperature of the emulsion occurred. 



It is true, however, that an alternative route was possible theoretically ; 

 that is to say, it is conceivable that after its discharge the current might be 

 deflected at a right angle along the surface of the fluid, and then pass down 

 between the side of the tube and the contained emulsion to the wire at the 

 bottom of the tube. But there was no indication that this route was followed, 

 and what we actually observed appeared to us to justify the conclusion at 

 which we arrived as to the direct passage of the current through the emulsion. 



In testing the effect of the discharges upon bacteria, the following was the 

 procedure followed : — The bacterial emulsion was prepared by rubbing up 

 two loopfuls of growth, generally taken from a 48-hours-old culture on agar, 

 with 10 c.c. of distilled water. When a uniform emulsion had been made, 

 a loopful of it was streaked out on each of two sloped nutrient agar tubes. 



