E. NEWTON HARVEY 283 



filtered off, washed quickly with water, and suspended in water, does 

 not completely dissolve. If luciferin is added the precipitate does 

 dissolve and a good light appears. Dilute NH4OH solution causes 

 the precipitate to dissolve. The filtrate gives a very faint light when 

 an excess of luciferin is added, even though everything was precipi- 

 tated that would precipitate with picric acid and an excess of the 

 latter was present. The excess of picric acid was not sufficient to 

 harm the luciferin used in testing. 



Luciferase is, therefore, completely precipitated by phosphotungstic 

 acid and almost completely precipitated by tannic and picric acids 

 without harm. 



Phosphotungstic acid added to a solution of crude luciferin to slight 

 excess gives a bulky precipitate which can be filtered off and the fil- 

 trate is perfectly clear. It gives no further precipitate with phos- 

 photungstic acid but contains a small amount of luciferin, as a faint 

 light appears when luciferase in excess (since luciferase is also pre- 

 cipitated by the excess phosphotungstic acid present) is added. The 

 precipitate washed on the filter with dilute phosphotungstic acid does 

 not dissolve completely in water but partly dissolves forming an 

 opalescent solution. It is brought into solution by adding crude 

 luciferase or a trace of dilute NH4OH solution. The precipitate con- 

 tains luciferin and gives a brilliant light with luciferase. It is prob- 

 ably the slight alkalinity of the luciferase solution which causes reso- 

 lution of the luciferin precipitate. The addition of a small amount of 

 HCl to the phosphotungstic-luciferin filtrate causes further precipi- 

 tation, 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. If an excess of tannic acid is present, as indicated by ab- 

 sence of further precipitate on adding more tannic acid, a small 

 amount of luciferin is present in the filtrate but practically all is 

 precipitated. The precipitate does not completely dissolve in water 

 even if NH4OH is added, but gives a bright light when luciferase is 

 added. The addition of a small amount of acetic acid -\- NaCl or 

 HCl does not cause further precipitation. Both the phosphotungstic 



