142 OUTLINES OF BACTERIOLOGY 



sugar become phosphorescent in slightly alkaline solutions. In these 

 cases the phenomenon of phosphorescence goes hand in hand with 

 the process of oxidation that takes place. It is assumed by this 

 theory, that the same process takes place in phosphorescent bacteria. 

 The theory is further supported by the facts that these bacteria are 

 luminous only in alkaline media, that phosphorescence is observed 

 in the presence of compounds that are either aldehydes or nearly 

 related to the aldehydes (e.g. the sugars) and finally that luminosity 

 is observed only in the presence of oxygen. Marine phosphorescence, 

 however, is more difficult to explain, for there cannot be sufficient 

 aldehydes or related bodies in the sea to produce the phosphorescent 

 effects that are there observed. 



The other theory is that the phosphorescence is a form of energy, 

 and does not emanate .from any particular substance. It is supposed 

 to be possessed by these bacteria, just as other plants possess the power 

 of movement, that is to say, phosphorescence is a vital phenomenon, 

 bound up with the living protoplasm and incapable of separation from 

 the same. This theory has fewer facts to support it than the other, 

 but it affords a better explanation of marine phosphorescence. 



The colour of the phosphorescent light is white or yellowish-white 

 and green or bluish-green. Further, the colour depends on the nature 

 of the nutrient medium and the position of the eye. Unlike the 

 spectrum of the sun, that of phosphorescent light is continuous, 

 that is to say, it is not interrupted by dark absorption lines and 

 bands. The spectrum extends in some species from b (green) up to 

 violet, and in other species from D to G, the blue and violet rays 

 being most prominent. The light differs from that of phosphorescent 

 animals in that it is steady, and a good culture may exhibit a 

 glow for months after inoculation. The phosphorescence from most 

 animal organisms, on the contrary, lasts only for a short time, a few 

 seconds or a few minutes, and in some cases is exhibited as a result 

 of an external stimulus. The light emitted by phosphorescent bacteria 

 suffices not only to photograph themselves, but also surrounding 

 objects. A darkening of the photographic plate can be effected by 

 laying it on the surface of a photogenic culture for as short a time 

 as one second. A more interesting practical application is the con- 

 struction of bacteria-lamps, and in the Paris Exhibition of 1900, a 

 whole room owed its light to the presence of a number of such 

 lamps. Their use as night-lights has been suggested, but an apparatus 

 of this description is more of a scientific curiosity than anything else, 

 and has not become a commercial success. 



