Aet. I. — The Influence of Light on Bacteria. 



By Arthur Downes, M.D., and Thos. P. Blunt, M.A. 



F.C.S. 



[Read 12th April, 1883.] 



In the Proceedings of the Royal Society of London (Vol. 

 XXVI., 1877, p. 488, and Vol. XXVIII., 1878, p. 199) we 

 reported the results of an investigation from which we con- 

 cluded that light is inimical to the development of Bacteria, 

 and, probably, injurious to " unprotected" protoplasm gene- 

 rally. 



Dr. J. Jamieson, in a paper recently read before the Royal 

 Society of Victoria, attacks our inferences, attributing the 

 observed effects not to light but to solar heat. 



We scarcely think that Dr. Jamieson can have seen the 

 text of our papers, or he would have noted that in nearly 

 every experiment of the long series special care was taken 

 to exclude so fundamental an error as that which he attri- 

 butes to us. 



Without troubling the Society with a long communica- 

 tion, we think that a consideration of two facts alone will 

 show that Dr. Jamieson 's criticism cannot be substantiated. 



In our experiments our usual method of procedure was to 

 place in each of a number of test-tubes a small quantity of 

 cultivation liquid. The tubes were then plugged with 

 cotton wool, loosely capsuled, and divided into two sets. 

 The one set were encased, each tube separately, in thin, 

 tarnished leadfoil (such as paperhangers use for damp walls) 

 so as to thoroughly exclude light. The two sets were 

 exposed side by side to full sunlight. When the insolation 

 was sufficient the uncovered tubes remained clear for an 

 indefinite period, while the encased speedily swarmed with 

 Bacteria. 



Now, if Dr. Jamieson will compare the temperature of two 

 tubes — encased and non-encased respectively — exposed to 

 the solar rays, he will find that the former becomes slightly 

 the hotter. 



