170 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



(b) Legal' s Reaction. Add a few drops of sodium nitro- 

 prusside solution (freshly prepared) till a distinct yellow color 

 appears, and then some drops of sodium hydroxide solution : 

 deep violet color. On acidifying with acetic acid the fluid 

 turns azure-blue. 



(c) So-called " Cholera-red Reaction." Very dilute indol 

 solutions, which also contain a nitrite, give a splendid 

 purple color with concentrated sulphuric acid. Cultures of 

 the cholera bacilli also give this color, as they contain both 

 indol and a nitrite. The nature of the coloring matter is not 

 known. To perform the reaction * add to 10 cc. of a very 

 dilute indol solution (containing 0.03 to 05 part per thou- 

 sand) 1 cc. of a 0.02 per cent, potassium nitrite solution, 

 mix thoroughly, and pour in some concentrated sulphuric 

 acid, so that it forms a layer on the bottom of the test-tube : 

 purple color. On neutralizing with sodium hydroxide solu- 

 tion the fluid turns blue-green. The reaction also takes 

 place on mixing with dilute sulphuric acid. When used 

 with cultures it is only to be regarded as proving the pres- 

 ence of cholera bacilli and some other kinds of bacilli, when 

 the sulphuric acid used is absolutely free from nitrous acid. 



CH S 



2. Skatol, Methyl Indol, C 6 H 4 



Colorless, shining leaflets, more readily volatile with steam 

 than indol, of a penetrating fecal odor, which is scarcely percep- 

 tible when the skatol is pure. Melting-point 95. More diffi- 

 cultly soluble in water than indol, readily soluble in ether, 

 alcohol, chloroform, and benzene. When introduced into the 

 organism it is oxidized to skatoxyl, which appears in the urine 



/OC 1 H N" 

 as potassium skatoxyl sulphate, 2 S<^Q K 9 ' , (Brieger). 



E. Salkowski; Virchow's Archiv, 110, 366 (1887). 



