THE EHRLICH DIAZO REACTION 333 



are taken iu medicinal doses and excreted in the urine the author says 

 there is no possibility of mistaking the reaction for the Ehrlich diazo 

 reaction. A large number of our patients have taken cascara for 

 weeks at a time without giving the reaction. It has been claimed 

 that the end-products of certain medicines excreted in the urine give 

 the diazo reaction. It is true that such substances as aniline, naph- 

 thalin, phenacetin, lactophenin, and orthoform give a color reaction 

 when treated with the diazo reagents. This has been called by a few 

 authors the Ehrlich diazo reaction. These were diazo reactions, but 

 not the Ehrlich diazo reaction. At the beginning of this article I 

 wish to emphasize the distinction between diazo reactions and the 

 Ehrlich diazo reaction. There are a large number of diazo re- 

 actions which are used to demonstrate certain known substances, 

 such as phloroglucin, acetone, bilirubin, naphthalin, grape-sugar, 

 peptone, and diacetic acid, while the Ehrlich diazo reaction is 

 used to demonstrate an unknown substance. In the former the 

 colors vary a great deal — purple, violet, blue, etc. — with a foam 

 which is not characteristic. Grape-sugar gives a beautiful fuchsin 

 pink color with an intensely red foam. The distinction, however, be- 

 tween the reaction and the Ehrlich reaction is that a fixed alkali is 

 required in the grape-sugar test, as it does not occur with ammonia. 

 It is the experience of every trained observer in a long series of 

 diazo tests with a great variety of diseases that countless varieties of 

 colors and tints have been obtained in the rings and the foams. By 

 the inexperienced many of these would have been called diazo tests. 

 These colors are yellow, brown, orange, and salmon, and mixtures of 

 the same. At times even the characteristic red ring is obtained, but 

 on shaking the essential characteristic pink foam is absent. Urea, 

 uric acid, kreatin, xanthin, sarcin, oxalic acid, hippuric acid, allantoin, 

 and urine rich in urobilin and indican do not give the Ehrlich diazo 

 reaction. Normal urine does not contain diazotizable substances. 

 In 1884, Ehrlich's work was confirmed in a series of experiments 

 by Lenhartz, of Leyden's clinic. Fisher, Brecht, Lowinson, Cnopf 

 and Grundies, Escherich, See, Dohrendorff, Goldschmidt, Loewe, 

 Georgiewski, Brewing, Roessingh, Piering, Riitimeyer, Simon, Ger- 



