1894.] on the Action of Light on Bacteria and Fungi. 279 



growing cells are compelled to begin or carry on their vegetative pro- 

 cesses in the light. This led me a short time ago to publish the 

 following opinions based on the facts even then to hand : — It seems 

 likely that pollen-grains, many fungus-spores and a large number 

 of such organisms as are exposed to light, are provided with the colour 

 screens they possess, and which screens are usually red or orange, or 

 some shade such as cuts out the blue-violet rays, as an adaptive protection 

 against the injurious rays of light. It is but an extension of this to 

 see in the green chlorophyll-screen of all our ordinary plants in part 

 a protection against the blue-violet rays of ordinary sunlight, the 

 ingress of which to the cell-contents would bring about destructive 

 changes of the order discussed in this lecture ; but we must not forget 

 that the chlorophyll-apparatus is more complex than this, and is 

 essential to the process of carbon assimilation, absorbing and making 

 use of the energy derived from the red-orange rays. 



In conclusion, it is impossible to put forward in a single lecture 

 all the results obtained, and still less the bearings of these results 

 and the experiments now being continued. I can merely say that 

 there is evidence to show that the slow and continued action of even 

 comparatively low intensities of light so act on these bacteria I 

 am working with that even where they are not killed, but only par- 

 tially injured by the inimical rays, their behaviour is so altered that 

 the resulting growths are perceptibly different from those of the same 

 organisms not exposed to light, that their powers of fermenting 

 organic substances are interfered with, and that various profound 

 morphological and physiological changes are induced in them. The 

 bearings of these matters — which are very complex, and the investiga- 

 tion of which is full of peculiar difficulties moreover, are so important in 

 regard to various questions concerning fermentation, the germ-theory 

 of disease and other departments of bacteriology, that I have no 

 hesitation in saying that no subject more vital to the interests of 

 mankind exists in the whole domain of biological science. 



[H. M. W.] 



