The Chemistry of Light-Production in Luminous Organisms. 189 



The concentrations of the two substances which will give visible 

 light when mixed are very small. In one experiment performed 15 min- 

 utes^ after the photophelein was obtained, 1 Cypridina in 25,600 c.c. 

 of water gave a just-visible light when mixed with an equal volume of 

 more concentrated photogenin. The photogenin from 1 Cypridina in 

 25,600 c.c. of water will also just give visible light when mixed with an 

 equal volume of more concentrated photophelein. 



We can see how small an amount of photogenin will give Ught when 

 we consider that the animal is about 3.5 by 2.5 by 1.5 mm. and that 

 the luminous gland is more or less of a cylinder 0.64 mm. high by 

 0.24 mm. diameter, with a volume of about 0.03 mm. or 0.00003 cm. 

 and that 1 luminous gland in 25,600 c.c. water will give visible light 

 when mixed with an equal volume of photophelein, or in a concentra- 

 tion of 51,200 c.c. Hence 1 part of gland in about 1,700,000,000 parts 

 of water will give visible light upon the addition of photophelein. 

 Even this is a low estimate, as we do not know what the concentration 

 of the photogenin is in the gland itself. 



When we compare the amount of photogenin which can be detected 

 by light-production with the amount of substances detectable by chem- 

 ical means, we see how extraordinarily sensitive the light-reaction is. 

 AgCl is soluble in water to the extent of 1 part in 625,000 parts water 

 at 20° (i4), so that more chloride than this must be present to be 

 detected by AgNOa, a very delicate reaction. KMn04 is roughly just 

 distinguishable by its color in a 14 mm. test-tube in a concentration 

 of 1 to 1,250,000. 



Biological reactions are, generally speaking, more deUcate than 

 inorganic reactions. Zinc in traces has a favorable influence on the 

 growth of molds and 1 to 25,000,000 will increase the weight of a crop 

 of Aspergillus by 50 per cent (is). Copper will kill Spirogyra in 

 1 minute when present in 1 to 77,000,000 concentration (is). Accord- 

 ing to Kastle (le), blood in 1 to 80,000,000 can be recognized by the 

 phenolphthalein reaction. Since this reaction is due to hemoglobin, 

 of which blood contains about 10 per cent, the hemoglobin can be 

 recognized in 1 to 800,000,000 concentration. These figures give an 

 idea of the delicacy of the photogenin-photophelein reaction as com- 

 pared with others. It should be borne in mind that pyrogallol in 

 1 to 254,000 will give visible light with potato-juice and H20a (see 

 p. 225). 



IS PHOTOGENIN USED UP IN LIGHT-PRODUCTION WITH PHOTOPHELEIN? 



The exceedingly small concentration of light substances which give 

 visible light suggests that one or both are of enzyme nature, as Dubois 

 supposes. There are two ways of testing this question. One is to 



^The experiment was performed as quickly as possible, because the photophelein disappears on 

 standing. 



