902 TftANSACTiOX.S OP SECTION K. 



effects; if tlie disinfectant employed is sufficiently dilute tlie reaction velocity of 

 disinfection can be studied by enumerating' the surviving bacteria after successive 

 intervals of time. 



The process is found to proceed in accordance with the mass law if 'number 

 of surviving bacteria' is substituted for 'concentration of reacting substance.' 

 The number of living bacteria, when enumerated after successive intervals of 

 time, is found to decrease in a logarithmic manner. Although disinfection in- 

 volves the interaction of two substances — bacteria and disinfectant — the reaction 

 velocity at any period during disinfection is controlled only by the 'concentration' 

 of living bacteria at the time. Disinfection thiis recalls a reaction of the 'first 

 degree,' the reason for this being that the concentration of the disinfectant may 

 be regarded as constant throughout, since it is present in so great excess. (An 

 interesting analogy is thus suggested with the case of sugar inversion.) 



The experiments npon which the above conclusions are based were made by 

 the author and other workers with both spore-bearing and vegetative types of 

 bacteria, and employing metallic salts, phenol, other coal-tar derivatives, and 

 beat as means of disinfection. 



The suggestion is made that the gradual and orderly nature of the disinfection 

 process is due to temporary differences in resistance among the individual bacteria, 

 which themselves may be referred to different rhythmic phases occupied by that 

 constituent of the bacterium concerned in disinfection. 



The reaction velocity of disinfection is influenced by temperature in a manner 

 similar to many chemical reactions, and increases logarithmically with rise of 

 temperature. With B. jjaratyphosus and metallic salts the increase was 2-4-fold 

 for a rise in temperature of 10° C. In the case of phenol the temperature coefficient 

 was much higher, between 7 and 8. 



3. Tlie Death-rate of Cells of Higher Plants in Fatal Conditions, 

 By Miss Nora Darwin and Dr. Blackman, F.R.S. 



4. Colour Changes in Flowers produced by controlling Insolation. 

 By Colonel H. E. Rawson, C.B., B.E. 



On March 12, 1905, a wonderful sunrise was observed at sea just after crossing 

 the equator while on a voyage from Southampton to the Cape of Good Hope. 

 Myriads of cirrus threads, as fine as gossamer, suddenly flashed out in the highest 

 levels of the atmosphere, and formed continuous and parallel lines of visible 

 vapour, converging optically to V-points, which were true north and .south as 

 the sun rose true east. The V-points did not remain fixed, but moved clockwise, 

 and the whole vault of heaven, with its countless arches of cirrus lines, swung 

 slowly round, as if on a pivot, in the zenith. 



The phenomenon did not disappear entirely for some days, and variations in 

 the disposition and movements of the threads in the cirrus level with respect to 

 bands of visible vapour, which formed at certain hours, in the cumulus and stratus 

 levels were noted and measured with instruments. 



While endeavouring to explain some of the effects, which were clearly attri- 

 butable to dii'ect rays from the sun, a crucial experiment suggested itself which 

 could most easily be carried out upon plants. 



On arriving at Cape Town Fome indication of the sun's action in the particular 

 direction suggested was looked for ajuongst garden plants, and was found in the 

 case of the Kei apple (Aberia caffra), which is much used for a border to gravel- 

 walks and flower-beds. This clue was followed iip, and experiments were carried 

 out in Pretoria with several different vegetables. These were found to be affected 

 by sun-rays in the way anticipated. 



The results obtained were described in a paper entitled ' Sunrise and Growth,' 

 which was read before the South African Association for the Advancement of 

 Science, and appeared in the Report for 1 905. 



