182 McDermott — Observations on a Photogenic Micro- organism. 



days the gelatin showed signs of being drier, and the culture 

 did not glow. A small portion of the gelatin was removed by 

 means of a spatula and placed in a Petri dish; it glowed feebly 

 in the air, the glow being just perceptible in a dark room. A 

 few cubic centimeters of 2.5 per cent hydrogen peroxide solu- 

 tion were then run upon the gelatin, when a number of bright 

 points showed for an instant, after which no glow was visible. 

 Attempts to completely dry liquid cultures, and to harden gela- 

 tin cultures in a hydrogen vacuum have so far been unsuccessful 

 on account of the leakage of the apparatus. Nitrobenzol, which 

 Dr. Kastle and the author found to be a powerful stimulus to 

 activity on the part of the luminous tissue of the firefly, was 

 without effect in stimulating the luminous activity of gelatin 

 cultures of this organism whose luminosity was on the wane, 

 and when added to liquid cultures promptly extinguished them. 

 A solution of sodium nitrite added to a liquid culture of Ps. 

 lucifera extinguished the light instantly. Both of these sub- 

 stances are germicides, and the results obtained are those which 

 would naturally be foretold. The addition of a few drops of 

 1 : 10,000 adrenalin hydrochloride solution to 20 c. c. of a 

 liquid luminous culture of this organism produced no immedi- 

 ate effect, but after 18 hours, the culture was apparently dead; 

 adrenalin was found to be a powerful stimulant of photogenic 

 activity in the firefly, when injected into the living insect. It 

 would appear, therefore, that in the firefly, these exciters act 

 upon the nervous system, and not directly upon the luminous 

 tissue. 



Oxygen under a maximum pressure of two or three atmos- 

 pheres was applied to a liquid culture in a closed bulb; the light 

 emitted became much stronger as long as the oxygen pressure 

 was maintained; sudden release of the oxygen pressure was 

 followed by a slow diminution of the intensity of the light. A 

 liquid culture placed in a desiccator rilled with hydrogen gave 

 no light after about five minutes; it also failed to give light 

 when treated with hydrogen peroxide at the end of three days, 

 when it had dried out to the point of crystalization. 



But little can be said as to the chemical processes by which 

 these organisms produce light. The process is certainly one of 

 oxidation, or at least one requiring the presence of oxygen, as 

 is the case with the firefly. Probably the actual use made of 



