DIGESTION. 217 



in close relationship to the indigo substances, and which are 

 formed from the albuminous bodies by their putrefaction, or by 

 fusion with caustic alkali. Hence they occur habitually in the 

 human intestinal canal and after oxidation into indoxyl and 

 skatoxyl respectively, pass, at least partly, into the urine as the 

 corresponding ethereal sulphuric acids, but also as glycuronic 

 acids. 



These two bodies have been prepared synthetically in many 

 ways. Both may be obtained from indigo by reducing it with tin 

 and hydrochloric acid and heating this reduction product with 

 zinc-dust (BAEYER). Indol may be formed from skatol by passing 

 it through a red-hot tube. Indol suspended in water is in part 

 oxidized into indigo-blue by ozone (NENCKI). 



Indol and skatol crystallize in shining leaves, and their melting 

 points are -j- 52 and 95 respectively. Indol has a peculiar excre- 

 mentitious odor, while skatol has an intense fetid odor (skatol ob- 

 tained from indigo should be odorless). Both bodies are easily 

 volatilized by steam, skatol more easily than indol. They may both 

 be removed from the watery distillate by ether. Skatol is the more 

 insoluble of the two in boiling water. Both are easily soluble in 

 alcohol, and give with picric acid a combination consisting of red 

 crystalline needles. If a mixture of the two picrates be distilled 

 with ammonia, they both pass over without decomposition ; but if 

 they are distilled with caustic soda, the indol is decomposed but 

 not the skatol. The watery solution of indol gives with fuming 

 nitric acid a red liquid, and then a red precipitate of nitroso-indol 

 nitrate (BAEYER). It is better to first add two or three drops of 

 nitric acid, and then a 2$ solution of potassium nitrite, drop by 

 drop (SALKOWSKI). Skatol does not give this reaction. An 

 alcoholic solution of indol treated with hydrochloric acid colors a 

 pine chip cherry-red. Skatol does not give this reaction. Skatol 

 dissolves in concentrated hydrochloric acid with a violet coloration. 



For the detection of indol and skatol in, and their preparation 

 from, excrement and putrefying masses, the main points of the 

 usual method are as follows : The mass is distilled after acidifying 

 with acetic acid; the distillate is then treated with alkali (to com- 

 bine with any phenol which may be present at the same time) and 

 again distilled. From this second distillate the two bodies, after 



