Harry Marshall Ward. 1X 
The labour required by the first two branches of the enquiry was enormous ; 
he identified and cultivated some eighty species ; the resulting answer to the 
second was happily in the negative. : 
As to the third, two facts were known. First, that river water, if stored, 
largely cleared itself of bacteria by mere subsidence; secondly, that 
Downes and Blunt, in a classical paper communicated to the Royal Society 
in 1877, had shown that exposure to direct sunlight is fatal to bacteria in a 
fluid medium. Ward showed that subsidence could not be entirely relied 
on, as the sediment might easily become the source of re-infection. The 
effect of sunlight required more critical examination. 
- It was known that the spores of anthrax were liable to be washed into 
rivers. Ward determined to study this as the most extreme type of 
pathogenic infection. As it is undoubtedly the most deadly micro-organism 
known,'and Ward proposed to deal with it on a large scale, it implied no 
small degree of courage. He found that the spores of anthrax were 
effectually killed by a few hours’ exposure to even the reflected light of a 
low winter sun. It was clear that this was due to the direct action of the 
light and not to any heating effect, apart from the fact that they will tolerate 
boiling for a few minutes. It was further shown that there was no 
foundation for the theory of Roux and Duclaux that death was due to 
poisoning by products of oxidation of the food-medium. Proof of this, 
indeed, was hardly required, for Pasteur had shown that the bacteria 
floating in the atmosphere are mostly dead. Were it not so, no surgical 
operation would be possible. To the bactericidal effect of sunlight is equally 
to be attributed the absence of bacteria from the High Alps. 
The next point was to ascertain to what rays the effect was due. The 
spores of anthrax are so minute that, when mixed in large numbers with 
gelatine, they do not affect its transparency. A plate of glass coated with 
the mixture is at first clear, but ceases to be so if kept in the dark, owing 
to the germination of the spores. Ward found, in fact, that a photograph 
could be printed with it, the darkening being the reverse of that of a 
silver plate. After experiments with coloured screens he completely 
solved the problem in 1893, with the aid of apparatus supplied by Sir 
Oliver Lodge and some advice from Sir Gabriel Stokes, by photographing 
the spectrum on such a plate. It was at once seen that the destructive 
effect was due to rays of high refrangibility, and, what was extremely 
important, extended to,and found its maximum in, the ultra-violet. Thesame 
results were obtained with the typhoid bacillus. He made the suggestion 
that the arc light might be used for the disinfection of hospitals and railway 
carriages. 
Comparatively little was known of the life history of any Schizomycete. 
Ward therefore made a detailed and exhaustive study of that of Bacillus 
ramosus, the Wurzel bacillus of German authors, which is common in 
Thames water, and bears a superficial resemblance to the anthrax bacillus, 
but is innocuous. It proved convenient for study, as it ran through its 
