338 Profs. Percy Frankland and Marshall Ward. 



FIG. 3. 



fore, was approximately the same as at the outset, and the dull light 

 seems to have prevented the usual rapid multiplication. 



The plate from B, made after exposure, gave us 680 colonies per c.c. 

 after two days' and 2550 colonies per c.c. after three days' incubation, 

 and showed evident signs of liquefaction. Here, therefore, it would 

 seem that the light had exercised an inhibitory action as to numbers. 



The plate from C gave 2268 colonies per c.c. after three days' in- 

 cubation, but it was liquefying still more rapidly. 



So far, therefore, with the dull light of a cloudy day, it did not 

 seem as if a.n exposure of four and a half hours gave results of much 

 significance as to the numbers of bacteria ; but it did seem as if the 

 plates from the exposed flasks showed less liquefaction. 



Meanwhile, the three flasks stood at a temperature of about 16 C. 

 overnight in the laboratory, and were exposed next day from 

 11.30 A.M. to 4.30 P.M. again a dull day, and practically no sunshine 

 at all. 



Before exposure, however, we took samples as before, and after 

 two days' incubation found that A had about 13,650 per c.c., B had 

 15,980 per c.c., and C was so badly liquefied that we could place no 

 reliance on the numbers (1584) counted. 



These numbers are not very satisfactory taken by themselves, but 

 they showed us that the matter was worth further investigation along 

 similar lines. 



The following table H summarises the foregoing facts : 



