56 COMPARATIVE PHYSIOLOGY 



yeast cells an " unorganised " ferment, zymase, capable of 

 effecting the same transformation previously identified with the 

 intact organisms. 



The foundations of modern knowledge of bioluminescence 

 were laid by Dubois in the eighties. Dubois' studies elicited 

 the following facts ; (i) when a preparation of the photogenic 

 organ of Pyrophorus is dipped in hot water, light-production 

 is irreversibly stopped ; (ii) when the fresh organ is ground 

 up the mass only glows for a short time ; (iii) if a hot-water 

 extract of the gland is added to a cold-water extract in which 

 all luminescence has ceased the production of light begins 

 again. This was also found to be the case in Pholas. Dubois 

 therefore advanced the hypothesis that the hot-water extract 

 contains a heat-stable substance, luceferm, which is oxidised 

 in the presence of an enzyme, heifer ase, present in the cold- 

 water extract. The latter can only go on glowing as long as 

 any luciferin remains unoxidised. Boiling the mixed extract 

 brings about cessation of light-production. Luciferin can be 

 obtained from Pholas by heating the viscous luminous secre- 

 tion to 70° C. or extracting for some hours in 90 per cent, 

 alchohol. 



Similar phenomena have been studied by Newton Harvey 

 in luminous bacteria, fireflies and other forms, especially in 

 the ostracod, Cypridina. The process involved has its parallel 

 in other biochemical reactions which can be carried out in 

 vitro. The glucoside, escuHn, in horse-chestnut bark is 

 oxidised in presence of haemoglobin and hydrogen peroxide 

 with production of light, and luminescence is also characteristic 

 of the oxidation of pyrogallol by the peroxidase of potato or 

 turnip juice. The oxidation product of luciferin can be re- 

 converted into its precursor by inorganic reducing agents. 

 We must recognise, therefore, three entities : {a) luciferin, an 

 oxidisable substance, heat-stable and dialysable ; {h) luci- 

 ferase, non- dialysable, destroyed by temperatures above 60° 

 and by tryptic digestion, an enzyme, probably of protein- 

 like constitution ; {e) oxyluciferin formed from {a) in pre- 

 sence of {h) with emission of light. As stated, oxyluciferin 

 can be reconverted by reducing agents into luciferin. 



