858 LUMINOSITY IN PLANTS. 



plants must be spoken of as a genuine vital luminosity. But in the 

 same way not long ag'o alcoholic fermentation was held to be insep- 

 arably connected with living yeast cells, wdiile to-day, thanks to the 

 brilliant biochemical discoveries of Buchner, we know that it is due 

 to a certain material — the ferment zymase — which can of itself, 

 although a lifeless substance, bring about the fermentation. We can 

 fiuppose the same to be true for photogen. Although the isolation of 

 such a luminous material has not as yet been accomplished, the fail- 

 ure is probably due to the material being present in such very minute 

 quantity, to its extreme iui^tability, and its destruction through the 

 death of the cell. What photogen really is, and whether the giving 

 of light represents a process of fermentation — these questions can not 

 at present be answered. The future investigator must unearth these 

 facts. To directly or indirectly prove the existence of photogen ; to, 

 if possible, isolate it from the cell, and then render it luminous — such 

 efforts, in the light of other biochemical facts, appear to me most 

 tempting and by no means unpromising. 



Whoever has observed the swarms of fireflies flying through the 

 darkness of the night like wandering stars, or the intense light of 

 pure cultures of bacteria and the higher fungi, must involuntarily 

 have been impressed by the peculiarity of these '' living " lights. 

 And therefore it is easy to see that at a time when the science of 

 physics has surprised us with unexpected revelations, appearing at 

 first like marvels, that we should with redoul)led activity turn our 

 attention to the nature of this light coming forth from life, and seek 

 to discover its physical, chemical, and physiological activities. 



I wish, first of all, to call attention to a noteworthy difference be- 

 tween the character of this light in the animals and in the plants. If 

 we leave out of account the Peridineae and confine ourselves to the 

 plants alone, we see they are always steadily luminous. The bac- 

 teria and higher fungi give forth light for days, weeks, months — in- 

 deed, under some circumstances, as when supplied with abundant 

 nourishment, for years, without cessation, day and night, wliile the 

 animals, with few exceptions, shine only a short time, a few seconds 

 or minutes, and mainly in response to some external irritation ; so 

 that the light gives the impression of a flash or spark. The light of 

 the fungi is of a white, green, or l)lue character, and, contrary to 

 earlier statements, never undulates like the light of phosphorus; never 

 is inconstant or glimmering, but is in all cases quiet, steady, and con- 

 stant, whether viewed with the naked eye or through the microscope. 

 As a rule, its intensity appears to be Ioav, and yet there are bacteria so 

 intensely luminous that they .can be seen on a bright day in the corner 

 of a room without the eyes being accustomed to the darkness. A re- 

 jnarkal)le object in this respect is Bacterium pho^ipJwream (Cohn) 

 Molisch, the luminous bacteria of butcher's meat, and, to an even 



