39G 



Prof. Marshall Ward. Experiments on the [Dec. 15, 



The following experiment may be selected as a type of the rest : 

 A (fig. 1) is the upright of an ordinary retort-stand ; on the ring B 

 rested a gelatine plate-culture of anthrax spores, covered with black 

 paper everywhere except the cut-out letter E, seen on its lower face. 

 C was an ordinary plane microscope-mirror, with its arm fitted to a 

 cork on A. 



The whole was placed in the middle of a field at Cooper's Hill at 

 9.30 A.M. on Wednesday, November 30, and exposed to the clear, 

 but low, sunshine which prevailed that day, the mirror being so 

 arranged (from time to time as necessary) as to reflect the light on 

 the E the whole period, until 3.30 P.M., when the plate was removed 

 and placed in the dark incubator at 20 C. On the following Friday 

 i.e., after less than forty-eight hours' incubation the letter E stood 

 out sharp and clearly transparent from the faint grey of the rest of 

 the plate of gelatine. Not a trace of anthrax could be found in the 

 clear area, even with the microscope, while the grey and almost 

 opaque appearance of the rest of the plate was due to innumerable 

 colonies of that organism which had developed in the interval. 



FIG. 2. 



It was impossible to incubate the plate longer for fear of liquefac- 

 tion, whence the sceptical may reply that the anthrax exposed to 

 light was only retarded; the experiments with agar show that such 



