1912.] Certain Results of Drying Non-sporing Bacteria. 



137 



rays. The slip was then transferred to a tube of litmus dextrose broth, and 

 incubated at 37° C. as usual. The object of carrying out the exposure in 

 nitrogen is to prevent the formation of ozone from the atmospheric oxygen, 

 which would per se be lethal. 



A second vacuum tube was then opened, the slip removed, and exposed in 

 the same way to the rays for 30 minutes, after which it was transferred to a 

 tube of litmus dextrose broth. No growth occurred in either tube, proving 

 that the action of the ultra-violet rays in an atmosphere of nitrogen had 

 been lethal. 



June 1. — Another of the same batch of vacuum tubes was opened, and the 

 slip transferred to litmus dextrose broth. A growth of B. pyocyaneus had 

 occurred within 24 hours. 



The details of the technique employed, which were devised by Sir James 

 Dewar, were as follows : The air admitted to the vacuum tube, after being 

 sealed off, was air which had been dried and deprived of particulate material, 

 by passing it through a U-tube containing cotton- wool, immersed in liquid air. 



The slip was transferred, with the film uppermost, to a capsule of German 

 silver, into which, near the bottom, a side tube was soldered, this being 

 connected with leaden tubing to a Dewar vessel containing liquid nitrogen, 

 from which the gas was regularly discharged by slow ebullition throughout 

 the experiment. 



The German silver capsule was fitted with a lid of quartz, and placed in a 

 beaker of pounded ice. The lid of quartz was made to fit fairly tightly 

 inside the upper part of the metal capsule, so that the nitrogen could only 

 slowly escape from the chamber. 



After two or three minutes to allow of the replacement of the air by the 

 nitrogen, the ultra-violet rays were switched on. The distance from the 

 horizontal quartz tube, whence the rays were emitted from the arc passing 

 between two mercury poles, to the top of the capsule was about 2 inches. 



May 26. — This observation was repeated in all details, upon slips of 

 Staphylococcus pyogenes aureus, which had been dried in vacuo for the five 

 preceding days, the connection with the bulb of charcoal, etc., being 

 maintained throughout. Tour tubes were sealed off, and on the same day 

 two were opened, the slips removed, and subjected, with the prepared side 

 upwards, to the rays, for 15 and 30 minutes respectively. After the 

 exposure, each slip was transferred to a tube of litmus dextrose broth. 



No growth took place in either tube. 



June 1. — A control vacuum tube sealed off on May 26, after five days' 

 connection with the bulb of charcoal and liquid air, was opened, and the 



