140 On the Luminosity of Midges. 



needs further discussion. This analogy, as also the last two 

 points, tends, however, to show that the cause also of the 

 luminosity is the same as in the case of Talitrus, and that, 

 consequently, we are here likewise confronted with an infection 

 by luminous micro-organisms. 



In order to convince ourselves of the justice of this 

 assumption, manifestly the simplest plan would be, as Giard 

 has done, directly to demonstrate the presence of the micro- 

 organisms. 



Herein, unfortunately, owing to the fact that the state of 

 preservation of the objects leaves so much to be desired, I 

 have not succeeded. 



I have attempted to employ various staining reagents for 

 bacteria (methylene-blue-eosin, gentian-violet. Gram's and the 

 Gram-Giinther method), but without obtaining a distinctly 

 positive result. 



It is true that in many cells of the fat-body, enclosed in 

 plasma, granules were to be seen which took a strong stain ; 

 but whether these are micro-organisms or merely some kind 

 of concretions or decomposition-products of the cells, it is 

 impossible to determine, so long as one is not in a position to 

 examine a fresh specimen, or, at least, preparations for the 

 purpose of comparison derived from the ordinary non-luminous 

 Chironomus. 



Manifestly the best proof would be the success of attempts 

 at infection, as in the case of Talitrus. 



As yet, therefore, we must forego, for a while, the final 

 decision of the interesting question as to the causes of the 

 luminosity of the midges, since all the points adduced are 

 to be regarded really as only indirect, not as direct, proofs; 

 and if I have ventured to decide in favour of the bacterial 

 cause of a phenomenon which has at present received so little 

 investigation, it is on account of two reasons : — 



1. Because I am convinced that the arguments which 

 have been adduced are still fairly weighty ones, and render 

 the bacterial origin of the luminosity at least in the highest 

 degree possible. 



2. Because I considered that any explanation of the 

 interesting phenomenon whatever, based upon facts, is at 

 any rate better than none. 



It was also my purpose once more to direct the attention 

 of naturalists to the phenomenon in question, and thereby, 

 perhaps, to stimulate someone to make a closer investigation. 



It appears to me to be possible that the luminous midges 

 also occur in Western Europe, as is already shown by the 

 observation of Brischke, isolated at present though it be. 



