388 ANNAL8 NEW YORK ACADEMY OF SCIEXGES 



except in the case of acetone. Neutralized sodium selenite proves to be 

 a very ineffective indicator for reduction. • The presence of sodium tetra- 

 borate inhibits to a very striking extent the reduction of sodium selenite. 



The reagent containing 3% sodium selenite, 10% sodium citrate and 

 10% sodium carbonate has been tested "with reducing sugars. Eeduction 

 with this reagent takes place, at 100° C, in one minute or even less. At 

 first a deep chlorine-yellow color is developed. After standing a minute 

 or two this color gives way to a light wine-red tint, then to a dense brick- 

 red precipitate, which fills the volume of the tube. A 0.02% solution of 

 glucose yields fair reduction, and in a 0.01% solution the reaction is still 

 evident, but faint. Solutions to be tested must be alkaline, and must not 

 contain potassium cyanid or oxidizing agents (free halogen, hydrogen 

 peroxid, potassium permanganate, potassium bichromate). Sugar-free 

 urine gives a positive reaction when it is acidified with hydrochloric. This 

 positive reaction is probably due to acetone substances and creatiain, 

 which decidedly reduce acidified solutions of sodium selenite. Proteins, 

 uric acid and creatinin do not interfere with the alkaline sodium selenite 

 reagent. 



Minute amounts of selenium in the form of selenite ion can be de- 

 tected by a procedure similar to that of the Marsh test for arsenic. One 

 milligram of selenium dioxid yields a characteristic dull red selenium 

 mirror, soluble in oxidizing agents. 



Eeductiox of Selenium Compouxds ix the Livixg Orgaxtsm 



plant substaxces 



Plant substances (apple pulp and potato pulp) bring about the reduc- 

 tion of sodium selenite to brick-red selenium. An alkaline reaction 

 favors the reduction process. Boiled material induces no reduction or 

 very faint reduction. 



YEAST 



Yeast reduces selenious acid, selenic acid and sodium selenite. The 

 red selenium deposits in the cell-body so that only the cells themselves 

 are pigmented, while the liquid above remains colorless. The cells can 

 be decolorized by washing with potassium cyanid. 



rxBOiLED :milk 



Unboiled milk in contact with a few drops of sodium selenite (room 

 temperature) will show reduction within one to three days; boiled milk 

 will show no evidences of reduction. Unboiled milk j^rotected with 

 toluol does not reduce as readily as milk exposed to the air. 



