PHOTOGENIN AND PHOTOPHELEIN.
Unlike the firefly, Cypridina, and Pholas dactylus, it is impossible to separate the luminous juice of Cavernularia into two substances, photogenin and photophelein (luciferase and luciferin), one destroyed by boiling, the other not, which will give light when mixed. We can not, for instance, cause light to appear in Cavernularia juice which has stood until the light has disappeared by adding fresh luminous Caver nularia juice heated to boiling and then cooled; neither can we obtain light by adding juice heated to temperatures below boiling (88°, 81°, 71°, 61°, or 52° C.) and then cooled.
The question may be asked, what substances are able to cause light to appear in the juice of Cavernularia which has stood until completely dark? Usually 4 to 6 hours are sufficient time for the juice to lose its luminescence. It is still capable of giving out a bright light if we add
fresh-water (but not sea-water) to it, and it retains this potentiality for over two days at 20° C. (see table 11) and a shorter time at higher temperatures. As only fresh water and not sea-water will call forth the light, and as we know that light-production is connected with the granules of the juice, the process appears similar to the cytolysis of cells—i. e., to the swelling and solution in fresh water of the granules which the cells contain. By this means something is liberated from the granules of Cavernularia juice which oxidizes with light-production. Table 12 gives the results of adding various other substances, pure or dissolved in sea-water, to the dark Cavernularia juice.
Note from table 12 that light-production is not due to dilution of the salts of sea-water by adding fresh-water, since m cane-sugar does not call forth the light. Note also that many cytolytic substances (chloroform, benzol, thymol, etc.) give light, but not the oxidizing agents, etc. The blood of certain invertebrates also causes very faint light-production, but we can not be sure that this is not due to the fact that the blood is somewhat less concentrated than sea-water, although the determinations of other closely allied forms show the salt-content to be the same as the sea-water in which they live.