AROMATIC METABOLIC PRODUCTS. 79 



may be distilled after adding MgO and the distillate 

 treated with Nessler's reagent. Yellow to reddish-brown 

 color indicates ammonia. Control experiments must 

 always be made. 



7. Aromatic Metabolic Products. 



Often, as the result of the action of very many varieties 

 of bacteria, there arise from albumin aromatic bodies, of 

 which indol, skatol, phenol, and tyrosin are best known. 

 Methodical investigations are at hand regarding the occur- 

 rence of only indol and phenol, since these bodies are 

 easily recognized. 



Demonstration of Indol. — ^There is added to the bouillon 

 culture, which is preferably not less than eight days old 

 and prepared without the addition of sugar, about one- 

 half its volume of 10% sulphuric acid. If, now, on 

 warming to about 80° a rose or bluish-red color at once 

 appears, then both indol and nitrite are present. The 

 nitroso-indol reaction Just described requires both these 

 bodies to be present for its success. AVith cholera and 

 most other vibriones, at times also with diphtheria, the 

 demonstration may be made (" cholera=red reaction"). 

 Usually the addition of sulphuric acid is not sufficient, and 

 it is necessary to add also a little nitrite. This may be 

 added if, upon warming without the nitrite, no reaction, 

 or only a doubtful one, is obtained. One adds 1 c. c. to 2 

 c.c. of a 0.05% solution of sodium nitrite until the maxi- 

 mum reaction is obtained. Addition of a stronger nitrite 

 solution colors the fluid brownish-yellow, and entirely 

 prevents the demonstration of indol. ' " 



Demonstration of Phenol. — The culture in non-saccharine 

 bouillon receives the addition of about one-fifth its volume 

 of hydrochloric acid and is then distilled. The distillate 

 gives a flocculent precipitate when treated with bromin 

 water. If carefully neutralized with calcium carbonate, 

 the addition of neutral very dilute chlorid of iron gives a 

 violet color. 



In sixty varieties examined, we found (see Table I) indol 

 production twenty-three times. Our findings accord well 

 with the statements of Levandowsky (Deutsch. med. 



