180 PHYSIOLOGICAL CHEMISTRY. 



ether. About 50 cc. of fresh ether must also be added. The mixture is 

 thoroughly shaken, separated as before, and the operation repeated until 

 all the acidified distillate is extracted. The ether is mixed with an equal 

 volume of water and enough sodium hydroxide to give a strong reaction. 

 The alkali combines with and holds the volatile acids which are present 

 while indol and skatol remain in the ether layer. Separate as before, 

 transfer the ether to a flask and distil at a low temperature. Drive off 

 three-fourths of the ether and allow the remainder to evaporate spontane- 

 ously. It will not be necessary to purify the residue in any way. Dilute 

 it largely with water and apply the following tests: 



Transfer 10 cc. of the dilute indol solution to a test-tube and add i cc. 

 of a dilute sodium nitrite solution, mix thoroughly by shaking and then 

 pour carefully a few cc. of strong sulphuric acid down the side of the 

 tube so as to form a layer below the other liquid. At the junction of the 

 two liquids a purple red color is formed, which changes to bluish green 

 on neutralization with alkali. This test is similar to the one commonly 

 employed in water analysis to detect the presence of indol-producing bac- 

 teria. The nitrite solution used must be very weak, preferably not over 

 0.02 per cent in strength. 



Another test is performed in this way. A splinter of soft pine wood 

 is moistened with strong hydrochloric acid and then dipped in a weak 

 aqueous solution of indol. The wood gradually becomes red. With much 

 indol the color becomes deep and characteristic. 



A characteristic test of value depends on the formation of a salt of 

 nitroso-indol. Acidify the indol solution to be tested with nitric acid and 

 then add a few drops of a 2 per cent solution of sodium nitrite. The 

 nitrate of nitroso-indol, Ci6Hi 3 (NO)N 2 HNO 3 , forms and produces a red 

 precipitate if much indol is present. If the indol solution is weak a red 

 color only forms. By adding some chloroform and shaking, the indol may 

 be concentrated in the junction layer between the two liquids. 



By adding a weak solution of sodium nitroprusside to an indol solution 

 a yellow color is first obtained. The addition of weak sodium hydroxide 

 changes this to violet, which, in turn, becomes blue by acidifying with 

 acetic acid. This is known as Legal's test. 



Skatol fails to give the above tests. 



OTHER PRODUCTS OF TRYPTIC DIGESTION. 



In the last few pages a brief summary of some of the most 

 easily recognized of the products formed in the pancreatic 

 digestion of proteins has been given. But the summary is by 

 no means complete, as the number of products obtained in the 

 protein disintegration is far larger than here suggested. Ac- 

 cording to the older views of peptic and pancreatic digestion 

 the amphopeptone of the stomach passes largely into antipep- 



