1893.] 



A ction of Light on Bacillus anthracis. 



33 



On the 29th the spores had germinated all over on both plates, and 

 the results were negative. This was probably in part due to the 

 exposure being too short. Nothing was gained by keeping the agar 

 plate another day. 



Of the other two plates, the agar preparation (Table III, F) was 

 exposed again daily till February 1 inclusive : this latter date was 

 the first sunny day ensuing, the intervening ones being dull or wet. 

 The other spore plate (Table III, H) was not put out till January 28, 

 as it was not quite dry on the 27th ; it received the same exposure 

 otherwise. 



On February 1 there were at least four hours' good bright sun- 

 shine — more probably, only I allowed for interruptions by clouds. 

 Other details may be seen by referring to Table III, E to H. 



On February 3 no trace of a letter could be detected on the agar 

 plate (Table III, F), and the spores sown thereon were germinating 

 evenly all over ; whereas a perfectly sharp and distinct C was visible 

 on the spore plate (Table III, H), although it had only been in- 

 solated for four hours instead of six. 



It is not necessary to detail all the confirmatory experiments, and 

 I will conclude with the following : — 



On January 29 I made three plates of agar alone and three of 

 spores (Table III, I to N), drying off the latter at 70° to 60° C. All 

 were left till January 31, because the 30th was a very dull day. 

 They were all put out on the 31st, but did not receive more than 

 15 — 30 minutes of interrupted sunshine at midday. February 1 was 

 a bright day, and each plate had at least four hours' direct sun. One 

 of each of the plates (Table III, I and N) was then incubated, after 

 receiving its reciprocal charge — agar on the spores, spores on the 

 agar. The others were left for further exposure. 



On February 3 the agar plate showed no trace of its letter (a 

 small B), whereas the spore plate showed a beautifully sharp +, the 

 shape of the area exposed, and over which the dry ripe spores were 

 killed. February 2 was a dull day, and the 3rd rainy, so that the 

 remaining plates got no sun until February 4, which was a beauti- 

 fully bright day, giving me at least five hours' clear sunshine. 



Two more plates, however (i.e., one of each kind, Table III, K 

 and M), were put into the incubator at 8.30 a.m. on the 4th, and 

 had therefore only received the four hours' real sunshine credited 

 to the preceding plates, though of course -they had been exposed to 

 two more days' diffused daylight. See Table III. I have recently 

 modified this procedure, however, to try to obviate the following 

 difliculty. 



I found that it is very difficult to pour the agar, &c, over the 

 film of insolated spores without sweeping some of the non -insolated 

 ones over the area left uncovered, and vice versa ; and, again, it is not 



VOL. LIII. D 



