168 CARNEGIE INSTITUTION OF WASHINGTON. 



Many hundreds of extracts of nonluminous forms have been mixed with 

 Cypridina luciferin in the hope of finding some form producing an enzyme 

 capable of oxidizing Cypridina luciferin with light production; also, non- 

 luminous animal extracts have been mixed with Cypridina luciferase in the 

 hope that some substance in these extracts might oxidize with light produc- 

 tion. In either case the results have been always negative. Extracts of non- 

 luminous forms do not react to produce light with Cypridina luciferin or luci- 

 ferase. They are neutral so far as effect on the Cypridina luminescence is 

 concerned, neither increasing or decreasing the intensity of this luminescence. 



However, one luminous form, Ptychodera, allied to Balanoglossus, does 

 inhibit the Cypridina luminescence. This animal, obtained in the sand under 

 rocks near Hamilton, Bermuda, produces, when irritated, a luminous slime, 

 whose light disappears rather quickly. If the slime, after the light has gone, 

 is added to a luminescent mixture of Cypridina luciferin and luciferase, the 

 Cypridina light is dimmed, or, if weak, disappears entirely. This is the only 

 instance that I have noted of inhibition of Cypridina luminescence by extracts 

 of other animals. The Ptychodera slime smells strongly of iodoform, but 

 whether the odor is really due to iodoform or not is unknown. Iodoform has 

 no effect on Cypridina luminescence, so that some other unknown material 

 in the Ptychodera extract is responsible for the inhibition. 



Reduction of Oxylttciferin. 



When luciferin oxidizes in presence of luciferase with light production, 

 oxyluciferin is formed. The oxyluciferin can be reduced to luciferin again 

 by various methods, and the luciferin ~ZZl oxyluciferin equilibrium is obviously 

 fundamental for the student of bioluminescence. This equilibrium can be 

 shifted toward the luciferin side in the presence of nascent or active hydrogen 

 produced in various ways, and conversely, under proper conditions, lumines- 

 cence may be used as a test for nascent or active hydrogen. Thus, if we 

 place a strip of Mg metal in a solution of oxyluciferin and luciferase, a lumines- 

 cence will appear over the surface of the Mg. The Mg dissolves in water 

 with the liberation of nascent hydrogen, which in turn reduces the oxyluciferin 

 near the metal to luciferin. The luciferin is then oxidized in presence of 

 luciferase and dissolved oxygen with light production. Other metals, as Al, 

 Mn, Zn, and Cd, also luminesce over their surface in oxyluciferin-luciferase 

 solution, despite the fact that no hydrogen, visible as bubbles, is given off by 

 these metals in water. A microscopic film of nascent hydrogen must be 

 formed over their surface which is replaced as it is used up in reducing the 

 oxyluciferin. 



The above-mentioned metals all stand low in the electro-chemical series. 

 If they are touched to any metal higher in the series, like Cu or Pt, and dipped 

 in salt solution, a galvanic cell is formed, in which the Cu or Pt act as local 

 cathode and reduction processes occur there. Consequently, if we touch with 

 Pt a piece of Zn immersed in a solution of oxyluciferin and luciferase to which 

 some NaCl is added to render it a conductor, the Zn ceases to luminesce and 

 the Pt luminesces brightly. Nascent hydrogen is now formed at the Pt 

 surface, reduces the oxyluciferin to luciferin, which is then reoxidized with 

 luminescence in presence of luciferase and oxygen. A whole series of metal 

 couples have been investigated and light appears at the cathode in accord 

 with expectation. 



