E. NEWTON HARVEY 289 



luciferin bound (combined or absorbed) in some way in the solution, 

 perhaps sometimes by causing cytolysis of still intact photogenic cells 

 or by causing solution of photogenic granules or granulysis. Extracts 

 of non-luminous animals sometimes contain substances acting like 

 the above cytolytic agents. For these I have suggested the general 

 term of photopheleins. Care has been taken to exclude such sources 

 of error and misinterpretations in the studies described below. 



It is obvious, from the method of preparation of luciferase, that, 

 should there be just enough luciferase or less than enough luciferase 

 to oxidize all the luciferin of a luminous gland, we could not obtain 

 a solution of luciferase by the above method. Only if an excess of 

 luciferase over luciferin exists can a solution of luciferase be obtained. 

 It is possible, therefore, that this is the explanation of negative results 

 for the presence of these bodies in certain groups of luminous organ- 

 isms, a possibility that can be tested in part and that will be discussed 

 below. 



It is not to be supposed that inability to demonstrate luciferin and 

 luciferase in a luminous form is always due to the same cause. Assum- 

 ing that luciferin and luciferase really do occur in all luminous forms, 

 it may be that they are present in such small amounts, compared 

 with the bulk of non-luminous tissue necessarily included in extracting 

 them, that no luminescence is visible. This might be the case in 

 ChcBtopterus, an annelid worm, where luminous gland cells occur over 

 the surface of the body. These cells cannot be removed individually 

 and the most luminous regions of the worm must be extracted as a 

 whole, involving a large mass of non-luminous material. 



Again, either luciferin or luciferase or both may be very unstable in 

 some forms, undergoing change before their presence in an extract 

 may be tested. 



Or, it is not impossible that the luciferase may occur in an endo- 

 enzyme condition, similar to the zymase of yeast or enzymes of 

 bacteria, which render it impossible to extract except under special 

 conditions and high pressures. I have concluded that such is the case 

 in luminous bacteria and that this explains the absence of a luciferin- 

 luciferase reaction in these forms. ^ It seems possible also, however, 



2 Harvey, E. N., Am. J. Physiol., 1916, xli, 449. 



