118 Influence of Light on Development of Bacteria. 



injurious effects supposed to have been produced by the 

 comparative exclusion of the sun's rays from parts of the 

 buildings. Though my investigations have not led me to 

 conclude that light is inimical to the development of bacteria, 

 I by no means wish to derive therefrom the further con- 

 clusion, that it is a matter of indifference whether or not 

 hospital wards, or other human habitations, are well lighted. 

 I do think it probable, however, that insufficient lighting 

 does not act, by allowing the free growth of disease germs, 

 and so favouring the origination or spread of erysipelas and 

 allied diseases. 



In the experiments, now to be described, I used Cohn's 

 solution, as in a series of investigations on the action of disin- 

 fectants, already communicated to this Society (11th October, 

 1877). This fluid, admirably adapted for the cultivation of 

 the Bacterium termo, the active organism in the production 

 of putrefaction, has the following composition : — 



Tartrate of Ammonia ... 2 



Sulphate of Magnesia ... 1 



Acid Phosphate of Potash 1 



Chloride of Calcium ... T V 



Distilled Water ... 200 



My ordinary procedure was to put about two fluid drams 

 of this solution into ordinary one-ounce phials, and, after 

 inoculation, plug them with cotton wadding. Free access of 

 air was thus allowed, while solid particles were excluded.. 

 A considerable series of experiments, sixteen in number, 

 were made to determine — (1) Whether ordinary diffused 

 light interferes in any way with the development of bacteria 

 in Cohn's solution ; (2) whether direct insolation has that 

 effect ; and (3) whether direct insolation quickly causes the 

 destruction of bacteria in the dried state. They were begun 

 in February last, and continued as other occupations 

 permitted. 



Exp. I. On February 21st three phials, inoculated each 

 with three drops of putrid meat juice swarming with 

 bacteria, were placed outside, on the sill of a window on 

 which the rays of the sun fell nearly all day. The weather 

 was very hot. On the 23rd all were still quite transparent, 

 and one was removed and put in a shady place. On the 

 26th this showed three specks of mould, but no opalescence 

 from bacteria. On the 28th the others left in the sun were 

 still perfectly transparent, and showed no mould formation. 



