Art. VII. — Influence of Light on the Development of 



Bacteria. 



By J. Jamieson, M.D. 



[Read 8th June, 1882.] 



It is a common opinion, and probably a correct one, that 

 abundance of light is favourable to the preservation and 

 restoration of health. In how far the evil effects, resulting 

 from the occupation of badly lighted dwellings, are due to the 

 want of light in itself or to other insanitary conditions, 

 damp, bad drainage, dirt, &c, which are often associated with 

 it, is not easy to prove with certainty. It has been supposed, 

 further, that the spread of epidemic and other contagious 

 diseases is favoured by conditions, which prevent the access 

 of the sun's rays to the walls and to the interior of ordinary 

 dwellings, and still more of hospitals, This unfavourable 

 result of shutting off direct sunlight has even been ascribed 

 to the effect of that light in destroying disease germs. Very 

 much of all this is simply matter of opinion, the supposed 

 destructive action of sunlight on germs being, perhaps, 

 assumed from the common observation, that the various 

 species of mould grow and multiply most freely in close, 

 dark, damp places. Even here, however, I am not aware of 

 exact observations or experiments having been made to test 

 the share that darkness, by itself, without the other con- 

 ditions, may have in favouring mouldy growths. 



Confirmation of the common opinion about the destructive 

 action of sunlight on those low forms of life, with which the 

 germs of some diseases are probably closely allied, seemed 

 to be supplied by the investigations of Messrs. Downes and 

 Blunt, reported in detail in the " Proceedings of the Royal 

 Society of London," for 1877 (vol. xxvi., p. 488). The general 

 conclusions to which they had come were summarised in a 

 short communication in Nature, for July 12th, 1877, to the 

 following effect : — Light is inimical to the development of 

 bacteria, and may either prevent or only retard their 

 development ; but that, for the attainment of the full effect, 

 direct insolation is necessary. The germs originally present 



