286 



Prof. W. M. Thornton. 



[June 20, 



vessel exhausted and filled several times with hydrogen passed through 

 sulphuric acid and tubes of soda-lime. An opening was then made by passing 

 a hot wire through the wax, and a continuous stream of gas sent past the 

 electrified needle from a cylinder of hydrogen. Fig. 18 (Plate 11) shows the 

 result of exposing plates of Conradi and Drigalski litmus lactose medium sown 

 with B. coli communis, which were before exposure inverted and dried in a 

 warm chamber to fix the emulsion on the surface. The jet of hydrogen 

 without ionisation was passed for three-quarters of an hour over one plate, 

 which was then removed. The electrostatic machine was then started and 

 the other plate exposed for the same time to the same stream of hydrogen, 

 now negatively ionised. The influence of the electrification is marked, 

 the area beneath the nozzle being quite cleared. This experiment is also of 

 interest in showing that pure dry hydrogen has no inhibiting effect on 

 bacterial growth. The conditions in this test were the most stringent that 

 could be devised. The surface of the agar was firm and dry and the time of 

 exposure short for so insensitive an organism as B. coli communis. The plate 

 may be compared with fig. 13, where the exposures were for half and one hour 

 using the same bacillus. 



The exposures in nitrogen and hydrogen were made in the Pathological 

 Laboratory of the University of Durham College of Medicine, under the 

 direction of Professor Hutchens, to whom, with his colleague, Dr. P. Laws, 

 the author is gratefully indebted. 



8. When bacteria are killed by any physical or chemical agency it is 

 generally accepted to be in consequence of the coagulation of protoplasm. 

 In the present case there are two immediate possibilities, apart from direct 

 electrical action, by which this might be achieved. The effect may be due to 

 the influence of ultra-violet light from the glow, or the mechanical bombard- 

 ment by the wind might be sufficient to produce inhibition of growth such as 

 is known to be caused by mechanical vibration. To put the first to the test 

 a piece of optical quartz, 2*4 cm. square by 1 mm. thick, was laid on the 

 surface of the agar, which had previously been sown with a strong emulsion 

 of B. asiaticce cholera: as a sensitive indicator. The dish was then exposed 

 for half an hour in such a position that the negative needle point was central 

 with the quartz square and at 1 cm. above it. The positive point was then 

 about L5 cm. from the edge of the square. At the. end of the exposure the 

 quartz was removed, care being taken to prevent liquid from the edges 

 flooding into the space occupied, though some unavoidably ran over the 

 space under the positive needle. The result on incubation is given on 

 the right of fig. 21. The growth on the part covered by the quartz is denser 

 than elsewhere, the space around showing evident signs of clearing. 



