LUMINOSITY IN PLANTS. 359 



greater extent, Psevdomonas luclfera Molisch, a photobacteriiim 

 which two years ago I discovered in marine fish, the light intensity of 

 which surpasses that of any hnninous bacteria heretofore know^n. 



To R. Dubois is due the credit of having first attempted to utilize 

 l)acterial light in the form of a lamp, and I have renewed Dubois's 

 attempt with the two already mentioned intensely luminous bacteria, 

 and have constructed a bacterial lamp on the following plan : In a 

 Florence flask, having a capacity of from 1 to 2 liters, is put from 

 200' to 400 cubic centimeters of salt-peptone-gelatin. It is then 

 stopped with cotton wool and sterilized. When cool, but before the 

 gelatin has quite solidified, it is infected with a culture, fresh and 

 luminous, of Bacterivm phosphorenm or Pseudomonas lucifera^ a 

 l^latinum needle being used. The flask is held horizontally and 

 slowly rotated, so that the gelatin forms a coating on the entire inner 

 surface of the flask and then hardens. After being kept for one or 

 two clays in a cool room, the entire inner surface of the flask is covered 

 with colonies of bacteria, so that it gleams wdth an exquisitely beau- 

 tiful bluish-green light, and presents with its soft, steady brilliancy 

 a splendid appearance. I have lately found that the luminous joower 

 of such a lamp can be considerably augmented by applying the 

 infection to the gelatin in parallel lines about 1 centimeter apart, 

 running from the bottom to the neck of the flask, and adding to the 

 gelatin 1 to 2 per cent of peptone and about one-half per cent of 

 gl^^cerin. Such a lamp will continue luminous in a cool room for 

 about fourteen days, and when the eye is accustomed to the darkness 

 Avill give light enough to see the face of a watch, the scale of a ther- 

 mometer, or to read coarse print. Such a flask is visible on a dark 

 night at a distance of CA paces, and could in an emergency be utilized 

 as a night lamp. Inasmuch as dead luminous flounders are success- 

 fully used as bait by fishermen on account of their light, a lamp of 

 this kind could be made to serve as a valuable lure in catching fish. 



My investigations warrant me in stating that in the future it will 

 probably be possible, by means of exact formulas of nutriment and 

 by selective breeding, to so increase the intensity of this exceedingly 

 cheap source of light, so free also from heat rays, that on account of 

 its cheapness, its long and uninterrupted luminosity, its freedom 

 from danger, and its lack of heat it can be turned to practical 

 account in powder magazines, in mines that are not too warm, and 

 in other j^laces. 



In connection with the investigations of F. Ludwig and Forster, I 

 may state, in regard to the lumiuous bacteria and mycelial fungi, that 

 their light spectra are continuous, without dark lines, and, as a rule, 

 simply luminous spectra — that is to say, on account of their low 

 intensity they are colorless; that the spectrum of the already named 

 bacteria shows a more decided trend tow^ard the violet end of the 



