Influence of Light on Development of Bacteria. 119 



Exp. II. On 28th February, at 11.40 a.m., an ounce of 

 solution was inoculated with twenty drops of putrid meat 

 juice, and distributed in four bottles. Two were exposed to 

 the sun, and the others, wrapped in brown paper, were 

 placed alongside of them. The weather was bright but cool. 

 On 3rd March both of the covered bottles began to show 

 cloudiness, and soon became quite opalescent. Next day 

 (4th), at 2.30 p.m., both of the exposed bottles were quite 

 transparent. One of them was then wrapped in paper, and 

 both left in the same place, but on the 6th they were still 

 transparent. 



So far these results seemed fully to confirm the conclu- 

 sions of Downes and Blunt. Direct insolation had not only 

 checked the growth of the bacteria, but had actually steril- 

 ized the solutions so far as they were concerned. The 

 survival of mould spores, after the destruction of bacteria, 

 also agreed with what these observers had found. 



I proceeded next to try what the effect of diffused light 

 would be. 



Exp. III. On 11th March, at 2.30 p.m., I inoculated six 

 drams of solution, with five drops of opalescent fluid from 

 one of the bottles left from a previous experiment, and dis- 

 tributed it equally in four bottles. Two were wrapped in 

 brown paper, and the others left uncovered, and all placed 

 in a bright light on an inner window sill, but guarded from 

 the direct rays of the sun. On the 13th, at 9 a.m., they 

 were all nearly opaque, no difference being perceived. It 

 was evident from this, that bright diffused sunlight is not 

 inimical to the development of bacteria. This experiment, 

 conclusive enough in itself, was confirmed by the next. 



Exp. IV. An ounce of solution, inoculated with four 

 drops of opalescent fluid from previous experiment, was put 

 into four bottles. Two were exposed to the sun ; one in the 

 same situation but wrapped in brown paper, and the fourth 

 left exposed to the light inside, at 2.30 p.m. on 15th March. 

 The temperature in the sun was noted at 110° F., and 

 next day at 112 c F. On the 17th, at 9 a.m., the wrapped 

 bottle and the one in diffused light were already cloudy, 

 the latter most distinctly. The two exposed bottles 

 were perfectly transparent, and both remained so till the 

 19th, at noon, though one of them had been taken out of 

 the sun. 



Having apparently established the fact that the bacteria 

 in Cohn's solution may be not only retarded in their develop- 



