Report on the Bacteriology of Water. 329 



changes in the intensity of the sun-light when direct on the 

 mirror. 



That the sluggishness in responding to the air-temperature is due to 

 the protection of the glass and the layer of water will be accepted at 

 once, I take it, and it will be equally obvious that the sharp rise in 

 direct sunlight is owing to the dark heat rays, reflected from the 

 mirror, passing easily through the red glass and water layer and 

 being absorbed direct. 



On the whole, then, we may conclude that so long as the culture- 

 cells are protected from the direct rays of the sun, the temperature 

 of their interior does not quickly vary, though it may be somewhat 

 higher than that of a thermometer outside. 



By keeping a thermometer, with blackened bulb, in such a culture- 

 chamber side by side with the growth culture under examination, 

 however, it may be accepted that the temperature of the growing 

 schizomycete in the hanging drop is very accurately known. 



Three culture chambers, with hanging drops of broth, were prepared 

 over-night, the only difference introduced being that I employed thin 

 quartz instead of glass for the floors. The spores germinated out 

 slowly, at 10 12 C. during the night, and the filaments began 

 growing more and more quickly as the temperature rose in the 

 morning. 



By 10 A.M. I had prepared a control or "dummy" cell, with the 

 blackened bulb of a thermometer in it, as described on p. 327, and 

 placed this beside two of the cultures, all in position on their micro- 

 scopes, at the south window. One culture was arranged for exposure 

 to light, and a thermometer (blackened bulb) hung to its microscope. 

 The other culture was arranged in exactly the same way, but kept 

 darkened by a dome of thick brown paper. 



The third culture was placed in a cooler room at a north window, 

 for growth at a lower temperature. At both windows ordinary ther- 

 mometers were also placed to give the air temperatures in the usual 

 way. 



Unfortunately the day turned out dull and cloudy, with rain 

 occasionally, but now and then the sun shone brightly at intervals 

 during the morning. 



The following tables give the results. Small thick cardboard slips 

 were arranged as shutters to prevent the direct sun-light from falling 

 on the mirrors or thermometers, &c., but with as little shutting off of 

 light as possible. 



VOL. LVIII. 2 A 



