LIGHT BY LIVING ORGANISMS—McDERMOTT. 855 
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 cucuyo. 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 thé majority of cases in which 
we used it. It has since been found by McDermott (°°) 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 (7) 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,O,, 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 contaiming 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. 
