176 Papers from the Department oj Marine Biology. 



All of the light-producing substances (both photogenin and photo- 

 phelein, p. 178) will easily pass a Pasteur-Chamberland or a Berkefeld 

 filter tube, so that the particles present, if any, must be exceedingly 

 small. 



Complete proof of the truly soluble character of the light-producing 

 substances is given by dialysis experiments recorded on page 183. 



LACK OF OXYGEN. 



Oxygen is necessary for light-production, as may be seen by placing 

 the crushed animals in a hydrogen atmosphere, or by bubbUng hydro- 

 gen through a glowing extract of the animals. The light never com- 

 pletely disappears, even after a long time, but remains dim, so that 

 very little oxygen (as no special precautions were taken to remove the 

 last traces of oxygen from the hydrogen, prepared in a Kipp generator) 

 is sufficient to give fight. On readmitting oxygen, however, a brilliant 

 glow results. Unlike the firefly (p. 196), an extract of Cypridina can be 

 kept in absence of oxygen for over ten days with no fight-production, 

 but fight again instantly appears if oxygen is readmitted. 



DESICCATION AND ETHER EXTRACTION. 



Cypridinas may be dried over CaCl2 and will give a brilliant fight 

 if crushed and moistened with sea-water. Dried crushed cypridinas 

 may be extracted with six changes of ether during the course of two 

 days without impairing in the least their power to produce light when 

 again moistened. The luminous substance is therefore of a non-fipoid 

 ether-insoluble nature, as might be expected from the fact that it is 

 extruded from the animal as a clear water-soluble non-fluorescent 

 secretion. 



CHEMICAL TESTS ON THE SECRETION. 



Despite the fact that the fight from the natural secretion of Cypridina 

 is very bright, a sample of the secretion, collected by shaking many 

 cypridinas in a small volume of sea-water and filtering, responds to 

 none of the common biochemical tests. It gives no precipitate with 

 picric acid or on saturation with (NH4)2 SO4 or on boiling, even when 

 made sfightly acid. Fehling's reaction is negative, as also the biuret 

 and xanthroproteic for proteins, the Mofish reaction for carbohydrates, 

 and the indophenol test (a-naphtholandpara-phenylen-diamine) +H2O2 

 for oxidases. 



I do not mean to infer from this that the luminous substance is 

 neither protein, fat, or carbohydrate, but merely that the concentra- 

 tion giving a bright light is too small to respond to chemical tests 

 (seep. 188). 



LUCIFERIN AND LUCIFERASE. 



The fight from the natural secretion of Cypridina lasts for some time 

 in sea-water and then disappears, and no amount of shaking will cause 



