Report on the Bacteriology of Water. 319 



It was evident that, provided I kept to the reflected rays from the 

 blue sky near the sun, the heating effect was about 2 3 higher 

 than in the open air beside the microscope, and that the cultures 

 between red glasses were exposed to at least about 1 or 2 higher 

 than those between the blue, orange, or green glasses, and these 

 facts must be carefully borne in mind when discussing the results. 



The hanging drops, each containing about 25 spores, were made at, 

 11.30 A.M., from broth, infected at 9 A.M., and. kept at 15 C., so that 

 the spores were already swelling and ready to begin germinating 

 when the cultures were exposed at 12.30 noon. 



As soon as the cultures were placed in position on the microscopes, 

 I turned each mirror so as to. powerfully iusolate each culture for 

 exactly five minutes ; that was all the direct sunlight they were 

 allowed during the whole period, except such rays as struck the top 

 glass obliquely, and the heating effect of which must be taken into 

 account in what follows. 



The results of the four examinations I roade of these cultures at 

 about 2.45, 4.45, 7.0, and 10.46 P.M. respectively, showed considerably 

 more growth in the red and orange than in the blue and green. 



The culture in diffuse light was an accident, and not part of the 

 planned series. It stood in a shaded part of the room, and was not 

 only at a higher temperature during the hours of exposure, but was 

 considerably more advanced to start with. It cannot, therefore, be 

 compared with the others, and must be regarded as merely of pass- 

 ing interest: its curve fell rapidly after 7 P.M., possibly owing to the 

 fall of temperature. 



Two hanging drop cultures of broth with a trace of gelatine, 

 of equal age spores sown at 10 12 C. over night were placed on 

 microscopes in the south window arranged as follows: The cells 

 had a thin glass floor. 



One had a sheet of red glass below, and a similar sheet above ; the 

 other a sheet of blue glass below, and screens of the same in front, 

 so that all light direct from the sky had to traverse the glasses 

 before reaching the drops. The only difference between the two 

 arrangements (apart from the colour of the glasses) was that the 

 first one had its second sheet of red glass close over the drop This 

 difference was necessary owing to the microscopes being of different 

 patterns. 



Unfortunately the morning turned out cloudy, with rain at inter- 

 vals, and occasional short breaks of sunshine ; a high wind kept the 

 temperature down to about 17 18 C., rising now and then to 

 1920 C. 



It will also be noted that I here exposed, not spores, but rodlets 

 already strongly germinated out. When the red culture was 

 started, at 10.46 A.M., the rudlet selected (to be kept under observu- 



