336 LUMINOSITY IN. PLANTS. [SEss. LXXII. 
a household occurrence, though perhaps luminous meat is 
not so familiar to us as luminous fish) is due to the presence 
of bacteria, usually B. phosphorewm. These phosphorescent 
bacteria, according to Fischer, are almost exclusively salt- 
water forms, and hence the readiness with which moist fish 
become luminous. Professor Molisch induced luminosity in 
meat by leaving it in a solution of salt in a cool place for 
a few days. A culture of phosphorescent bacteria can be 
made in a 2°3 per cent. NaCl solution, besides the ordinary 
salts and peptone, and also some source of carbon, such as 
sugar, ete. 
The same author in his work on Luminosity, has sug- 
gested luminous bacteria as a source of illumination. By 
inoculating glass flasks containing a suitable culture medium 
with phosphorescent bacteria, he obtained a “ bacterial lamp ” 
with which it was quite possible for an observer at a distance 
of one or two meters to read a thermometer or see the time 
of a watch. It has been suggested that such a lamp might 
be used in a powder magazine, or for attracting fish, as the 
flask might be sealed up and lowered into the water, since 
dead luminous flounders have been successfully used by 
fishermen as bait. Professor Molisch says that to RK, Dubois 
is due the invention of this bacterial lamp. 
Beyerinck has done much interesting work in connection 
with phosphorescent bacteria. He has shown that they can 
be used as an extremely delicate test for oxygen, in the 
smallest trace of which these bacteria become phosphorescent. 
He has also used them for detecting the presence of an 
enzyme. ; 
Let us now briefly consider the theories that have been 
suggested as an explanation of the phenomenon of luminosity 
in plants. That luminosity is in some measure connected 
with respiration is undoubtedly the case, for, generally speak- 
ing, if the oxygen supply be cut off, luminosity ceases. That 
it does not, however, vary directly with respiration is proved 
by the fact that respiration increases up to a maximum 
temperature, whereas luminosity ceases above a rather lower 
optimum temperature. Massee maintains that luminosity 
is a specific property of the protoplasm and not simply due 
to oxidation. There seems, however, far more in favour of 
Pfeffer’s view that certain substances are probably produced 
