66 Ward. — A Violet Bacillus from the Thames. 
a couple of hours’ exposure on a spring day. I have also 
attained fairly satisfactory results in bright sunshine by placing 
a plate behind an ordinary photographic negative : the print 
was slightly wanting in sharpness, because of course I had to 
have a plate of sterilized glass between the agar-film and the 
negative ; but in cases where the glass was thin enough the 
picture was very good indeed. 
Tubes of water containing large quantities of this Bacillus, 
can be almost completely sterilized by a few hours’ exposure 
to sunshine. No doubt the question of temperature comes in 
in all these cases, but it must be noted (i) that I have kept 
them alive for four or five hours in a hanging-drop at 30 to 
35° C., and (2) that in the experiments with the solar and 
electric spectra, where the exposures are made over ice, the 
maximum light-effect is not towards the red end at all, but 
in the blue- violet. I therefore regard these bactericidal effects 
as due to the blue-violet light-rays, and not to the high 
temperature. 
I have made numerous attempts to watch and measure the 
growth and division of the rodlets, but although I have been 
able to convince myself that the filaments segment up into 
the short rodlets, the fact that both filaments and rodlets are 
moving actively in all the available media, as soon as the light 
is turned on them 1 , though in some cases at any rate they 
seem to become quiescent again in the dark, has completely 
baffled all my endeavours. These movements seem to depend 
on a fairly high temperature — 20 to 25 0 C. or so — and I should 
say the divisions are completed about every twenty minutes 
or so 2 . The shorter segments (Bacilli) often move actively, 
each for itself, before separating from the other segments — 
rarely more than four in all — of the filament, which has a slow, 
undulating movement as a whole. I have not investigated 
the question of cilia, but the character of the movements of 
1 This fact had already been observed by Engelmann (Unters. aus dem Physiol. 
Lab. zu Utrecht, 1882, p. 252). 
2 Brefeld (Bot. Unters. IV, p. 46) found that B. subtilis, at 24 0 R. and under 
favourable conditions, divided once every thirty minutes. 
