358 Profs. Percy Frankland and Marshall Ward. 



in spite 01 the fact that not all the cells were killed by the insolation 

 (see below). 



For my own part, I regard it as more probable that the high tem- 

 perature merely helped the light action, for if the death was due to 

 the high temperature, why did not all the cells die ? That some 

 escaped is intelligible if they were sheltered behind others a by no 

 means improbable event, for the culture was an advanced one, be it 

 noted whereas it is not easily explained on any assumption of 

 heating or of poisoning. 



It will be useful again to summarise the results of the foregoing 

 section, and the suggestions they give rise to, before proceeding 

 further. 



1. So far as the spores exposed in the ripe resting condition are 

 concerned, it may be regarded as proved that the blue-violet rays can 

 retard or kill them, apart from any temperature effect, and it is 

 shown that they are extremely resistant to high temperatures. 



2. As regards actively growing bacilli, the evidence goes to show 

 that the light action affects them also, by retarding their growth, 

 and even eventually killing them, but, owing to certain difficulties, it 

 is not so clearly shown quantitatively how far the effect is due to 

 light alone, because the retarding effects are not observable within 

 the short period during which measurements are taken. 



3. In attempting to trace the effects of light (of moderate intensity 

 only) it is so difficult to keep two growing filaments exactly at the 

 same temperature under different conditions of illumination, that the 

 quantitative results cannot be insisted upon too much in detail, for 

 there is always the suspicion that even a difference of less than one 

 degree of temperature may affect the rate of growth, and therefore 

 alter the steepness or otherwise of the curve. 



4. Some results suggest the possibility that the organism may even 

 make use of rays at the red end of the spectrum in combatting the 

 effect of those at the blue end. 



5. The further possibility is suggested that the difference of 

 behaviour between the spores and the filaments may simply depend 

 on the relative activity of the protoplasm that when the latter is 

 comparatively inactive, as in the resting spore, it is incapable of 

 resistance to the light action, but that, when it is actively engaged in 

 metabolism and growth, it can resist the action if the temperature is 

 favourable, and the more so the nearer the optimum the temperature 

 is. On the other hand, extremes of temperature may favour the 

 light-action. 



6. Yet another hypothetical step may be taken. It is possible 

 that the spores succumb so readily simply because a dangerously 

 unstable supply of easily oxidisable materials is there, ready to be 

 destroyed by the light-action ; whereas, it is conceivable, these food- 



