306 



Profs. Percy Frankland and Marshall Ward. 



experiments could not be regarded as satisfactory ; whence it was 

 necessary to again have recourse to gelatine cultures. The gelatine 

 employed began to run at 29° C, and in November it was found that 

 such plates exposed outside, either to directly incident sunshine, or 

 to directly reflected rays, showed a temperature of 12° to 13° C. at the 

 insolated glass surface, and even five to six hours' exposure caused no 

 running of the gelatine. 



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 



Fig. 2. 



