On the Chemistry of Light Production in Luminous Organisms. 101 
Basic lead acetate gives a voluminous heavy precipitate with crude 
luciferin. After heating, the solution was filtered and the clear filtrate, 
which gave no further precipitate with basic lead acetate, gave a 
brilliant light with luciferase. The precipitate washed twice with 
water on the filter does not dissolve in water, but suspended in water 
gives a faint light on adding luciferase. Uranium nitrate + acetic acid 
does not completely precipitate luciferin from solution. These results 
are recorded in table 3. 
Luciferin is therefore not completely precipitated from solution by 
mercuric chloride with or without acetic acid, neutral lead acetate, or 
basic lead acetate, or uranium nitrate and acetic acid. 
ACIDS AND ALKALIES. 
As alkalies (KOH or NaOH in small, NH,OH in greater concentra- 
tion) precipitate the Mg of sea-water, this salt should be removed from 
a crude solution of luciferin and luciferase before studying the precipi- 
tating effects of these substances. This can be done by the addition 
of a small amount of sodium pyrophosphate, which forms Ca and Mg 
pyrophosphates, insoluble in water. The precipitates are removed by 
filtration and the photogenic substances are found unharmed by the 
addition of pyrophosphate. 
Neither luciferin nor luciferase are precipitated by addition of dilute 
NaOH or dilute NH,OH to their crude solutions, first rendered free of 
Ca and Mg. 
Dilute acetic acid added to luciferase solution gives a fine precipitate 
which is filtered off and washed with running water for 24 hours. It 
does not dissolve completely in water and gives only a faint light with 
luciferin. The precipitate is probably a mucin and carries down some 
adsorbed luciferase. The filtrate is perfectly clear, gives no further 
precipitate (sometimes a slight cloudiness on standing) withacetic acid, 
but a bright light with luciferin. The addition of slightly more acetic 
acid results in a clear filtrate giving no light with excess luciferin. The 
precipitate on the filter does give a faint light with excess luciferin, but 
appears to be injured by the acid. 
Saturation with CO, causes a precipitation in crude luciferase solu- 
tion, but the filtrate gives a brilliant light with luciferin. 
Dilute acetic acid added to concentrated luciferin gives a stringy 
precipitate. If filtered off, the filtrate is slightly opalescent, but does 
not become more cloudy or precipitate if more acetic acid is added. It 
gives a bright light if luciferase is added to it. The precipitate does not 
completely dissolve in water, butif washed with water and suspended in 
water gives a fair light with luciferase. This precipitate is probably a 
mucin containing some adsorbed luciferin. In the luminous gland of 
Cypridina there is a material which stains as does mucin, and it would 
