136 PHOTOGENIC REACTION IN CYPRIDINA 



tates and colloidal particles, such as bone-black, Fe(0H)3, kaolin, 

 and others. If we take a colloidal Fe(0H)3 solution of the proper 

 concentration (which can only be determined by experiment), add 

 some dilute lucif erase to it, and then after a minute luciferin, no light 

 will appear. This is because the luciferase has been completely ad- 

 sorbed by the colloidal Fe(0H)3, for if we now add some dilute luci- 

 ferase to the above mixture light will appear but it will very quickly 

 disappear because the new luciferase added is again very rapidly ad- 

 sorbed, but not so rapidly adsorbed that we fail to get light at first. 

 On adding more luciferase we may again get a momentary light but 

 the additions cannot be made indefinitely because we finally reach a 

 point where the colloidal Fe(0H)3 has become saturated with luci- 

 ferase and then the mixture glows for a considerable time. It is ob- 

 vious that for this experiment to succeed there must be more luciferin 

 present than can be completely adsorbed by Fe(0H)3 and so little 

 luciferase present that it is completely adsorbed by the Fe(0H)3. 

 Suppose we have a mixture of Fe(0H)3, luciferase, and luciferin com- 

 pl)dng with the above conditions. Can we in any way remove the 

 luciferase from its adsorbed condition on the colloidal Fe(0H)3? 

 This might theoretically be done in two ways and we actually find in 

 practice that both methods are possible. Anything which precipi- 

 tates the colloidal Fe(0H)3 will decrease the surface available for 

 adsorption of luciferase and if the surface area is sufficiently de- 

 creased some luciferase may be forced into solution again where it is 

 able to oxidize the luciferin. If we add NaCl crystals to the col- 

 loidal Fe(0H)3 -|- dilute luciferase + more concentrated luciferin 

 mixture, the Fe(0H)3 is precipitated and light appears. If in place 

 of NaCl crystals we add a trace of saponin, the colloidal Fe(0H)3 

 is not precipitated but Hght also appears. This is an example of the 

 second method of removing luciferase from an adsorbed condition; 

 namely, by using a material (saponin) which is more strongly ad- 

 sorbed than the luciferase and which is able to replace it as adsorbed 

 body. I believe these to be the explanations of the effect of NaCl 

 crystals, saponin, etc., in giving light with luciferase solutions, ex- 

 cept that the luciferase is in excess and a small amount of adsorbed 

 (or combined) luciferin is present which is liberated by NaCl or 

 saponin and gives light with luciferase. Photophelein probably acts 

 in a manner analogous to the saponin. 



