12 Dr. & the Rev. S. Graham Brade-Birks— 
and he concluded that it was not merely oxidation in progress 
that produced the light ; he found that the secretion stopped 
glowing if dried and began glowing again on the addition 
of water. The secretion was acid, and so the hypothesis of 
Radzizewski, which explained animal luminosity as a slow 
oxidation in an alkaline medium, is shown, Dubois says, to 
be incorrect. Dubois considered that the oxygen permitted 
the respiration of the protoplasmic corpuscles passing from 
a colleidal to a crystalline coudition—that is, from life to 
death; hydrated protoplasm is needed for the proper activity 
of this respiration, and water is necessary for crystallisation 
to take place under conditions favourable to the emission of 
light. Oxygen serves to produce the crystallisable sub- 
stance and water allows of photogenic crystaliisation. These, 
he maintains, are two successive states of one and the same 
substance, modified by oxygen and water. ‘This substance 
he terms luciferin. 
Dahlgren (4), passing the work on Juminous centipedes in 
review, mentions some of the researches we have already 
noted. He also records (4c) that Thomas found a species 
of Geophilus being attacked by ants. The centipede was 
throwing out masses of slimy light material which adhered 
to the ants. 
Up to the time of our own thirteenth paper (2) we were 
not familiar with living luminous centipedes, and in our last 
paragraph on the subject of luminosity we spoke of our 
familiarity with Geophilus carpophagus, Leach, in South 
Lancashire, mentioning that we had never noticed it luminous 
there. In Kent itis commonly luminous. We thereupon 
concluded that the phenomenon was hardly likely to be in 
any way essential to the well-being of the animals, but that 
it seemed more likely to be due to conditions of nutrition 
and environment, a view which seemed to be supported by 
the fact that Keut observers who had kept some luminous 
centipedes in captivity found that their powers of exhibiting 
phosphorescence upon stimulation gradually declined, and 
generally disappeared in the course of three days. . 
From the foregoing accounts of observations and opinions 
it will be seen that chaos must reign in the reader’s mind 
after perusing the literature. The next section of this 
paper, which deals with our own observations, is intended 
to gather together the main threads of our knowledge of the 
subject, and to indicate the lines upon which subsequent 
research should proceed. 
As early as 1862, Phipson published a book (11) on 
‘Phosphorescence,’ in which a short chapter is devoted to 
