1892.] Action of Light on Bacillus anthracis. 399 



p 1, p 2, and p 3 showed in each case a perfectly clear central patch, 

 about 1J inches diameter, with anthrax colonies in the gelatine 

 around. These anthrax colonies were the larger and more vigorous the 

 more distant they were from the clear centre. In other words, the 

 anthrax spores had begun to germinate, and the colonies were 

 growing more vigorously, in centripetal order. 



Onp 7 andp 8 germination was beginning, but the colonies were as 

 yet too young to enable one to judge of the results. 



The first point of interest is to account for the pronounced results 

 in the plates ^5 andp6, and the want of sharp outlines injpl, p2, 

 andp3, and the explanation seems to be that, owing to the plates 5 

 and 6 having laid over night at 16 C., the spores began slowly to 

 germinate out, and were consequently in their most tender condition when 

 exposed to the sunlight next day. 



The peculiar centripetal order of development of the colonies on 

 plates j?l, p2, and p 3 gave rise to the following attempt at explana- 

 tion. After observing that the clear space in the middle was not due 

 to the centre of the plate being raised, and the infected gelatine 

 having run down to the periphery a possible event with some batches 

 of Petrie's dishes it was surmised that the large letters employed 

 might give the clue. 



This was found to be the case. The solar rays on entering the 

 plate were largely reflected from the glass lid of the plates, and so 

 produced feebler_.insolation effects on parts of the plate around,. the 

 letter : these effects were naturally feebler and feebler towards the 

 margin, and so the inhibitory action became less pronounced at dis- 

 tances further and further removed from the centre. Those spores, 

 therefore, which were nearest the periphery germinated out first, 

 and those nearer the centre were retarded more and more in propor- 

 tion to their proximity to the insolated letter. 



That this is the correct interpretation of the facts follows clearly 

 from the further behaviour of the above plates. 



At 10 P.M. on the llth i.e., twelve hours after the morning ex- 

 amination the plates pi, jp2, and p3 exhibited their respective 

 letters M, H, and B quite clearly, in the grey matrix of anthrax 

 which had rapidly developed in the interval, and excepting a slight 

 want of sharpness in the H of p 2, the results could hardly have been 

 more satisfactory. 



In p 7 and p 8 the very faint outlines of the letters were also 

 showing. 



On the 12th, at 8.30 A.M., the gelatine plates had begun to run, and 

 although the M of p 1 was still intact, and very well marked, p 2 had 

 liquefied completely, so that the H was a clear patch with blurred 

 outlines in the centre, p 3 sfcill showed the outlines of the B, but it 

 was impossible to keep it longer. 



