On the Chemistry of Light Production in Luminous Organisms. 99 
NH,OH solution. The precipitate contains luciferin and gives a 
brilliant light with luciferase. Itis probably the slight alkalinity of the 
luciferase solution which causes re-solution of the luciferin precipitate. 
The addition of a small amount of HCI to the phosphotungstic-luciferin 
filtrate causes further precipitation, leaving a clear supernatant fluid 
containing no trace of luciferin. 
Tannic acid likewise gives a voluminous precipitate with luciferin 
solutions and the filtrate is clear at first but may become cloudy in a 
short time, especially at the surface, unless considerable tannic acid is 
added. Ifan excess of tannic acid is present, as indicated by absence of 
further precipitate on adding more tannic acid, a small amount of luci- 
ferin is present in the filtrate, but practically all is precipitated. The 
precipitate does not completely dissolve in water, even if NH,OH is 
added, but gives a bright light when luciferase is added. The addition 
of a small amount of acetic acid ++ NaCl or HCI does not cause further 
precipitation. Both the phosphotungstic and tannic acid precipitates 
can be dried and will again give light with luciferase if redissolved. 
Picric acid added to luciferin solution gives no good precipitate, but 
only an opalescence or turbidity. This is true even when picric acid is 
present in considerable excess,as on addition of an equal volume of 
saturated aqueous picric acid. A little dilute acetic acid or HCl does 
not cause precipitation. The solution filters turbid and luciferin may 
be demonstrated in the filtrate on adding luciferase. A yellow light 
due to the picric acid in solution appears. A little dilute NH,OH clears 
the turbidity. 
If we add acetic acid to luciferin solution until the precipitation 
(probably a precipitate of mucin) is complete and then dilute K,Fe 
(CN). solution, no further precipitates form and luciferin is found 
abundantly in the filtrate, which gives no further precipitate with 
K,Fe(CN), and acetic acid. The results are recorded in table 3 (p. 110). 
Luciferin is, therefore, very nearly completely precipitated by phos- 
photungstic and tannic acids, but not by picric acid. It is completely 
precipitated unharmed by phosphotungstic acid + HCl, but not by 
tannic acid + HCl or picric acid + HCl. It is not precipitated by 
potassium ferrocyanide and acetic acid. Dubois! finds Pholas lucif- 
erin to be completely precipitated by picric acid. 
HEAVY METAL SALTS. 
Some of the heavy metal salts (Pb acetate, AgNO;, CuSO,) precipi- 
tate in sea-water. As both crude luciferin and luciferase solutions, 
although prepared with distilled water, contain small amounts of the 
salts of sea-water, a slight precipitate would be formed upon addition 
of lead acetate. It is too small in amount to interfere with the action 
1 Dubois, Ann. Soc. Linn. de Lyons, 1913. 
