Influence of Light on Development of Bacteria. 117 



are destroyed by direct insolation, while the fitness of the 

 solution in which they were contained, to serve as a nidus, 

 is not affected. They used Pasteur's solution, inoculated 

 with bacterial germs, and then exposed to direct sunlight in 

 test tubes. The experiments described seemed to bear out 

 their contention, though the results were not of a uniform 

 character. They found an exposure of 3J hours suffice for 

 sterilization in one case, while in another it was not produced 

 after 11 hours. They could suggest no other explanation 

 than "that external conditions — notably temperature — may 

 retard or counteract the preservative quality of the solar 

 rays." Remarkably enough, they found that in weak 

 solutions, diluted to one-tenth, they failed to accomplish 

 sterilization. Professor Tyndall read a communication before 

 the Royal Society on the same subject (Proceedings, vol. 

 xxviii., p. 212), in which he stated that when flasks, contain- 

 ing infusions of cucumber and turnip, were inoculated and 

 exposed to the sun, they were not completely sterilized, as 

 they showed abundant formation of bacteria after they were 

 removed to a warm room. In view of the anomalies which 

 had been met with by Messrs. Downes and Blunt, and the 

 different conclusions he had arrived at, he suggested the 

 necessity for repeating the experiments. In the same 

 volume of the Proceedings (xxviii., p. 199), there appeared 

 another paper by these gentlemen, extending and confirming 

 their conclusions. Finally, at the meeting of the British 

 Association in 1881, Professor Tyndall read a paper {Nature, 

 Sept. 15th, 1881), in which he gave the results of another 

 series of experiments. He found the statements of Messrs. 

 Downes and Blunt correct, in so far as the suspension of 

 development was concerned, but he never succeeded in pro- 

 ducing perfect sterilization, all the flasks exposed to sunlight 

 becoming turbid when removed to a shady place. He 

 expressed the definite opinion that the difference between 

 flasks exposed to the sun, and those kept in the shade, after 

 inoculation, was not owing to difference of temperature. 

 It seems to have been tacitly assumed, both by him and by 

 the other investigators, that any elevation of temperature, 

 to which their tubes and flasks were liable in the course of 

 their exposure, could only be favourable to bacterial growth, 

 and merely noting this fact, I go on to relate my own 

 experiments, which have brought me to different conclusions. 

 I was led to make them by the discussions going on as to 

 the sanitary condition of the Melbourne Hospital,, and the 



