LIGHT BY LIVING ORGANISMS McDERMOTT. 355 



Thus far one substance alone has conducted itself as a positive 

 inhibitor of the photogenic function. This is sulphur dioxide. 

 Carradori observed this fact with the Luciola italica over 100 

 years ago, and Dubois has made a similar observation with regard to 

 the eucuyo. The live insect, the freshly detached luminous organ, 

 and the dried tissue, placed in this gas, all fail to glow, or glow but 

 weakly and momentarily, and are dead to all other stimuli when 

 removed from it. As a rule even those substances which tend to 

 poison the luminous tissue caused the evolution of a dim light at 

 first, but not so with sulphur dioxide in the majority of cases in which 

 we used it. It has since been found by McDermott ( 50 ) that liquid 

 sulphur dioxide and liquid ammonia both destroy the photogenic 

 power of the dried tissue. 



Mechanical stimuli, such as friction and percussion, and physical 

 stimuli, such as electricity and heat, also cause the production of 

 light by the luminous organs of the firefly, whether attached to the 

 living insect or detached. The effects of various temperatures and of 

 electric discharges of various strengths have been extensively studied 

 by other observers. Lund's ( 42 ) observations on the effect of heat 

 on the tissues are very interesting and important, as showing definite 

 temperatures as the fatal points for light production, reduction of 

 O s 4 , etc. Transferring the detached luminous organs from one gas 

 to another, even though one or both be chemically neutral, may cause 

 light production, apparently due to some osmotic effect. Currents 

 of air and other gases exert an effect on these detached organs, which 

 Prof. Kastle has compared to the effect of air currents on the strych- 

 ninized frog. It is obvious from these facts that the luminous tissue 

 is one of great irritability. 



Some of these results indicate that the effect of reagents is exerted 

 on the nervous system rather than directly on the luminous tissue, 

 and this probably accounts for some of the irregular and conflicting 

 results obtained by those who have experimented in this field. 



The significant fact that osmic acid is reduced by the luminous 

 tissue has already been referred to. It has been observed that 

 fixing fluids containing this oxide increase the intensity of the light 

 of fresh luminous organs placed in it, but whether this is due to direct 

 oxidation by the osmic and chromic acids present, or to irritation 

 of the nervous system produced by them, can not be said. 



The writer has observed that liquid luminous cultures of Pseu- 

 domonas lucifera are extinguished and killed by the addition of solutions 

 of hydrogen peroxide and sodium perborate, and of mononitrobenzene, 

 but that the effect of adding solutions of potassium perchlorate was, 

 if anything, to increase the intensity of the light, and the culture was 

 not killed in two days. 



