Report on the Bacteriology of Water. 



309 



distinct veil of colonies all over it on the 9th, and this had developed 

 to a dense typical growth by the 11th. 



On December 11, at 10 a.m., the state of affairs, as regards the 

 exposed plates, was as follows : — 



po and p6 showed each a sharp transparent letter — E and I 

 respectively — of clear agar in a dull grey matrix of strong anthra2 

 colonies, which covered all the unexposed parts of the plate. 



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

 about li- 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 

 authrax spores had begun to germinate, and the colonies were 

 growing more vigorously, in centripetal order. 



On p 7 and p 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 p 5 andp6, and the want of sharp outlines in pi, p 2, 

 audp'3, 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 p 1, 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 11th — i.e., twelve hours after the morning ex- 

 amination — the plates pi, p2, 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 slighs 

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

 more satisfactory. 



VOL. Lin. Y 



