348 Profs. Percy Frankland and Marshall Ward. 



tion of the rise in temperature between 10.40 and 12.30, hefore germi- 

 nation had begun be it remembered, and therefore acting on spores 

 which will bear a high temperature, e.g., 60 C. for some hours. The 

 order of germination ought to have been (1) bichromate, (2) water, 

 (3) dark, and (4) CuS0 4 culture, whereas it was (1) bichromate, 

 (2) dark, (3) Cu.SOj, and the spores behind water did not germinate 

 at all, but were there lying dead. 



In order to settle the doubt as to temperature, or sudden slight 

 alterations of temperature, being the cause of the retardation and 

 death of the spores, I repeated the experiment on the following day, 

 exactly as before, excepting with the single modification that the 

 table was so placed that no direct sunshine whatever was allowed to 

 fall on the apparatus or spores ; they received no light except that 

 from the blue sky and white cumulus clouds passing through the 

 liquids and glass. 



The results, summarised in the table and curves (pp. 350, 351, and 

 353), show that my conclusion was right; the effect is solely an effect 

 of the lip lit passing through the screens. 



The accompanying table (p. 349) gives the temperatures, during 

 exposure, of the liquids, the air in the dark bell-jar, and the cells. At 

 4 P.M. the cells were all brought into the laboratory and kept under a 

 dark jar. The temperatures during the night and following day are 

 also recorded. The differences in temperature are so slight that the 

 spores may be regarded as exposed to the same conditions as 

 regards heat. Nevertheless the red and dark cultures germinated 

 out five or six hours before the blue, and were much stronger and 

 more rapid in growth, while the spores under water were killed, and 

 all this with only five hours' exposure to diffuse light from a blue 

 sky, which was, moreover, slightly hazy for a considerable part of the 

 time, and never entirely free from white clouds. 



This experiment seems conclusive. Moreover, it is instructive in 

 other respects. It shows, for instance, that when the dark heat raj s 

 (transmitted by the bichromate the day before) are absent, the 

 bichromate culture germinates out and grows like that in the dark, 

 and that these rays are not necessary for the bactericidal effect 

 through water. That the culture behind the CuS0 4 germinated out 

 at all is no doubt due to the thick layer of strong CuS0 4 diminish- 

 ing the quantity and intensity of the light ; it is pretty certainly a 

 mere matter of length of exposure. 



It seems to me the importance of these results can scarcely be 

 over-estimated in their bearing on the question of the death of 

 bacteria in water. As the sun shines for a longer time and with more 

 intensity on the river day by day with the advance of spring to 

 summer the spores will be more and more retarded, and even those 

 which escape actual death with the advent of the night are again 



