PHYSIOLOGY OF THE MICROBES 91 



Certain fishermen employ as bait luminous fragments of dead 

 fish, a luminous bait provided by bacteria. 



With the aid of the spectroscope, Molisch distinguished in 

 the light of Pseudomonas lucifera the colours green, blue and 

 violet. R. Dubois photographed colonies of these bacteria with 

 their own light alone. Although feeble this vegetable luminosity 

 exerts, like sunlight, heliotropism ; the shoots of young plants 

 such as vetches, peas and lentils turn towards it on germinating ; 

 but it is incapable of exciting the chlorophyll function. 



Substances which kill the microbe abohsh its luminosity. 

 Dubois stated that he had isolated a substance which shone on 

 contact with the oxygen of the air, luciferine, but others failed 

 to repeat this experiment. It is possible that the microbe 

 secretes a substance which as soon as it is produced is 

 destroyed by oxidation giving out in the process luminous rays. 

 Many organic substances, aldehydes, ethereal oils, carbides 

 of hydrogen, fats, and alcohols, when they combine with free 

 oxygen in an alkaline medium, can emit light closely resembling 

 that of the above bacteria ; perhaps the bacteria give out 

 light thanks to the oxidation of substances in the cell, such 

 as lecithin, cholesterin, and ethereal fats ; but there is one 

 difficulty : the living cell does not contain free oxygen. 



To prove that the luminosity of bacteria is a chemical 

 phenomenon independent of the life of the cell which pro- 

 duces it, it would be necessary to repeat with these bacteria 

 the experiments which have been made with the secretions 

 of certain animal cells. With the photogenic substance of 

 Luciola italica one can write, and the writing becomes 

 luminous whenever it is moistened. If the luminous organs 

 of Lampyris noctiluca, which have been dried and preserved 

 in vacuo, are moistened with a drop of distilled water, the 

 luminosity reappears. Paper soaked in the secretion of 

 certain Myriapods can shine when moistened, even after two 

 months. In these cases the luminosity cannot be attributed 

 to a living cell. 



Bacteria which have never been exposed to light shine quite 

 as well as those grown in daylight. Their luminous property 



