252 THE INFLUENCE OF LIGHT ON LIFE. 



sunshine no doubt plays some part in producing that result, and 

 he relates how two German students proved, by examining the 

 water in a certain river from six o'clock in the evening till six 

 o'clock in the morning, that the numbers were increased enor- 

 mously during the dark hours of night, and that when the light 

 returned in the morning the numbers were reduced again. An 

 experiment is quoted which showed that in a certain small quan- 

 tity of water, where there were at the surface 2,100 bacteria, three 

 hours' sunshine reduced the number to only nine, whereas in dark- 

 ness a similar number increased to 3,103. The destroying influence 

 of light i2L\\'mg perpendicularly does not extend to much depth in 

 the water. The organisms at the bottom of the quantity just 

 referred to were scarcely lessened in numbers. They were, how- 

 ever, prevented from increasing. 



It may just be fair to state that I tried the experiment of 

 " sunning " an infusion of hay to see if the Bacillus subtilis would 

 be destroyed or hindered in the development ; but I regret to say 

 that they appeared to develop more rapidly than some which were 

 kept in the dark. My trial was a failure, but it cannot be regarded 

 as proving anything, for I feel sure it was not conducted properly. 

 The amount of hay in the tube would no doubt prove a sufficient 

 shelter for the organisms from the sun, and would therefore defeat 

 the very object in view. I might have tried the experiment again, 

 but was compelled to give it up in disgust, as the sun would not 

 shine when it was required to do so. When the experiment was 

 so far in train the sun would suddenly disappear for, perhaps, a 

 couple of days, and then reappear when it was too late. It is 

 satisfactory to note, however, that other gentlemen have had equal 

 troubles on this score, as they occasionally speak in a sort of 

 resigned tone of the advantages of experimenting under a more 

 favourable sky than we are blessed with. However, this does not 

 alter the wonderful results which have been found to follow inso- 

 lation (that is, exposure to the sun's rays), and it certainly ought to 

 move us to consider the possibilities which may be within our 

 reach when our knowledge of the subject is further advanced, and 

 to regard the sun as a benefactor whose bounty can scarcely be 

 fully appreciated. 



No doubt the purity of the air, and to a certain extent also of 



