332 UNIVERSITY OF COLORADO STUDIES 



phoid fever and tuberculosis. Unfortunately, in his earlier contri- 

 butions Ehrlich gave very meagre and unsatisfactory directions 

 regarding the preparation of his reagents, with the result that differ- 

 ent investigators of ability experimented in a blind way with the test 

 and arrived at erroneous conclusions. Peuzoldt, Petri, and von 

 Jaksch declared that it could be obtained in numberless diseases and 

 conditions, even in normal urine; that all sorts of bodies, such as 

 grape-sugar, acetone, bile-coloring matter, and a number of medicines 

 would give the same reaction, and considered the test worthless as a 

 prognostic and diagnostic measure. Among American authors Mun- 

 son and Oertel deny its diagnostic worth, claiming that diacetic acid 

 is the cause of the test, and that its diagnostic and clinical signifi- 

 cance must be identical with the ferric chloride test. Instead of us- 

 ing a ^ per cent, solution of sodium nitrite, as recommended by 

 Ehrlich, these investigators used as high as a 5 per cent, solution. 

 Greene found that when he used a concentrated solution of sodium 

 nitrite a reaction similar to the diazo was obtained even in normal 

 urine. 



Mistakes were also made in the interpretation of the test. Ed- 

 wards regarded the junction -ring — eosin to garnet — as the Ehrlich 

 diazo reaction, and found it in so great a variety of diseases and con- 

 ditions that he considered it useless as a diagnostic or prognostic 

 sign. Edwards made the fatal mistake of disregarding the crucial 

 part of the test, the color of the foam. Every investigator of experi- 

 ence is familiar with the fact that a red ring of varying tint is ob- 

 tained in countless diseases. This, however, is no more the Ehrlich 

 diazo test than a colored precipitate is Fehling's test. 



A misunderstanding as to the exact color of ring and foam nec- 

 essary for the production of a genuine Ehrlich diazo reaction has 

 perhaps been the most prolific source of error. Burghart, for 

 instance, claims that if tincture of opium, cascara sagrada, or hydras- 

 tis canadensis be added to urine a reaction similar to the diazo is ob- 

 tained. I experimented with these drugs and found that the only 

 one which suggested in color the diazo reaction at all was tincture of 

 opium, which gave a salmon tint to the foam. When these drugs 



