318 Profs. Percy Frankland and Marshall Ward. 



1 1- 



Before proceeding to the results obtained by exposure behind 

 coloured screens, I select the following series of further experiments, 

 which confirm some of my previous statements, referred to above 

 (Table A). 



It is worth remark that these exposures were made in February, at 

 a time when the temperature was low, and the sunlight, though 

 bright, of an intensity far below that obtainable in the summer. The 

 methods of preparing the agar plates and films of dried spores, 

 have already been described, that is to say, in experiments num- 

 bered D (1), E (1), J (1), C and D, a plate of sterile agar was 

 exposed, in each case behind a stencil plate, and, after exposure, was 

 laid flat on a film of dried unexposed spores of B. anthracis, whereas 

 in the cases marked otherwise it was the film of spores which was 

 thus exposed, and a sterile plate of unexposed agar then placed on 

 the film. Incubation then decided whether the light had produced 

 any effect, the results being given in the table. 



These results fully confirm those obtained previously, and show 

 that the action of the light is direct on the spores, and not on the 

 food material in this case agar in which the spores are suspended. 

 That the slow development in the cases marked H (1) and I (1) was 

 due to deficient aeration possibly in part also to the fitful sunshine 

 to which the plates were exposed is borne out by the following 

 experiments. Three stout glass tubes were selected, sterilised, and 

 charged each with about 5 c.c. of bouillon, in which was distributed 

 a small loop-full of the spores of B. anthracis. Each tube was about 

 6 in. long, and, after charging, was plugged with sterilised cotton 

 wool, the plug being pushed 2 in. into the tube. Each tube was then 

 drawn out to a point, exhausted of air, and the end sealed in a flame. 

 The vacuum tubes were kept thus sealed until the following day, 

 when two of them were broken at the tips, in a flame, to let in air ; 

 the other remained sealed. 



The sealed tube, and one of the now unsealed tubes, were then 

 exposed all day to a bright sun, while the third (unsealed) tube was 

 wrapped in tin-foil and black paper, and placed side by side with the 

 others, thus protected from the light. After six or seven hours' expo- 

 sure, the tip of the still sealed tube was also broken, and all three 

 placed in the incubator at 22 C. 



In forty-eight hours the covered tube and the exposed sealed tube 

 were equally and copiously turbid, with a vigorous growth of the 

 bacillus ; the exposed unsealed tube showed the faintest traces only of 

 this turbidity. 



The inference is obvious. Exposure to sunlight in vacua results in 

 no perceptible retardation or destruction of the bacillus, whereas if 



