2 The Influence of Light on Bacteria. 



This in itself disposes of his theory that the germinal 

 matter in the non-encased tubes is destroyed by solar heat ; 

 for if that heat were sufficient for such a result, it should 

 obviously suffice also for the destruction of germs contained 

 in the encased cultivation liquid. 



Professor Tyndall, in repeating our experiments, is forced 

 to the same conclusion, namely — that the energy which here 

 prevents putrefaction is energy in the radiant form. 



Secondly, Dr. Jamieson will find in the second of the 

 papers in the Proceedings of the Royal Society details of 

 experiments which distinctly show that the waves of 

 greatest refrangibility are the most active ; in other words, 

 to use the old phraseology, that the effect is associated 

 chiefly with the " actinic" rays. This fact, which may readily 

 be substantiated by any one who will carefully repeat our 

 experiments, must again prove that Dr. Jamieson's supposi- 

 tion of heat destruction is quite untenable. 



Art. II. — The Influence of Light on Bacteria. 

 By James Jamieson, M.D. 



[Read 12th April, 1883.] 



At the meeting of this Society on 8th June last I read a 

 paper on this subject, in which I detailed the results of 

 certain experiments, made for the purpose of testing the 

 conclusions arrived at by Professor Tyndall, and by Messrs. 

 Downes and Blunt. I was led at first to agree fully with 

 these gentlemen, that the effect of exposure to the sun's rays 

 of solutions inoculated with bacterial germs is to prevent the 

 development of the bacteria. Continued observation, how- 

 ever, showed me that the fullest exposure to diffused light 

 has no such effect ; and, further, that long continued exposure 

 to the direct rays of the sun need not have that effect. 

 Finding, also, that insolation seemed to fail when the 

 temperature was moderate in degree, I was led, perhaps 



