Report on the Bacteriology of Water. 307 



At 2.20 P.M. the thermometer in both bell-jars stood at 23 C., and, 

 as the curve of temperature shows, they were so nearly equal 

 throughout the experiment that I had little hesitation in concluding 

 that the cultures did not vary much from the same temperature nt 

 any time ; because I thought it could hardly be imagined that the 

 hanging drops in these damp cells rapidly vary with the tempera- 

 ture of the environment, aud still less so the filaments growing in 

 them. 



At 2.30 the observations were begun by noting the temperature, 

 and measuring the rod in each case. As the following tabular record 

 shows, the difference in time between the two notes rarely exceeded 

 a couple of minutes, whence the two series are closely comparable in 

 all respects. 



It was not until much later that the question arose or, rather, 

 acquired the great importance I now attach to it how far the culture 

 in the light could avail itself of or be affected by the infra-red rays 

 reflected from the mirrors, and so complicate the matter of tempera- 

 ture effects in these experiments. This matter is of pregnant im- 

 portance iu its bearing on all physiological experiments of this kind, 

 however. 



