SECRETION 57 



Conversely the luciferin of Pholas can be oxidised with emission 

 of light by various inorganic oxidising agents, e.g, hydrogen 

 peroxide, potassium permanganate. This is not true of the 

 luciferin of Cypridina, which differs in other respects from 

 that of Pholas, being in particular more heat-stable. Whether 

 the luciferases of different animals are identical is not wholly 

 certain ; in Cypridina the presence of luciferase is confined 

 to the photogenic organ. Apparently luciferase — or luci- 

 ferases, if there are several of such substances — belongs to 

 the category of enzymes known as oxidases which catalyse 

 other oxidative processes in the body. 



To sum up, photogenic response in at least three groups 

 of luminous animals, beetles, molluscs, and Crustacea, involves 

 the interaction of two readily separable components which 

 have entirely different chemical properties. Probably, how- 

 ever the " luciferins " and '' luciferases " of different animals 

 are not identical. Thus the luciferin of Cypridina differs 

 from that of Pholas in that it cannot be oxidised with light- 

 production by H2O2 and KMnOi- The luciferase of Cypri- 

 dina differs from that of Pholas in being less readily destroyed 

 by lipoid solvents. When the luciferin of Cypridina is 

 oxidised, no dissolution of the molecule takes place, since the 

 product can be readily reconverted into its precursor by such 

 reducing agents as H2S or nascent hydrogen. The luci- 

 ferases are destroyed by proteoclastic enzymes, and are to be 

 regarded as oxidases either themselves of protein constitution 

 or adsorbed to proteins in solution. 



Electric Organs.— Under the heading of secretion reference 

 may conveniently be made to the electrical organs which are 

 present in several genera of fishes, since in one genus at least 

 (Malapterurus) the electric organ is a modified gland, though 

 in other cases the cellular elements have been derived from 

 muscle fibres. These phenomena serve to draw attention to 

 a property which gland cells share in common with other 

 excitable tissues, namely an electrical response accompanying 

 excitation. The existence of an electrical charge accompany- 

 ing excitation is well illustrated by the experiments of Anrep 

 and Harris on pancreatic secretion induced by secretin, and 



