THE AROMATIC OXY-ACIDS. 269- 



hydrochloric acid to which a 0.5 per cent, solution of sodium 

 nitrite has been added in the proportion of 1 : 40, and the mixture 

 is then rendered strongly alkaline with ammonia, a more or less well- 

 marked orange color develops. Under pathological conditions, on the 

 other hand, and notably in typhoid fever, a red color results which 

 varies in intensity from a light carmin to a deep garnet-red. This 

 reaction is known as Ehrlich's diazo-reaction, as it is dependent 

 upon the presence of a diazo-compound of the nature of diazo- 

 benzene-sulphonic acid in the reagent. This results through an 

 interaction between the sodium nitrite and the sulphanilic acid, as 

 represented in the equations : 



(1) NaNO 2 +HC1 =HNO a + NaCl. 



NH, , / N x 



Sulphanilic Diazo-benzene- 



acid. sulphonic acid. 



I briefly refer to the reaction at this place, as v. Jaksch has 

 expressed the opinion that in " most " cases it is referable to the 

 presence of acetone, and in reality represents only an uncertain test 

 for this substance. This statement I wish to contradict most 

 emphatically, as I have been able to show beyond a doubt that 

 Ehrlich's reaction quite commonly occurs at a time when abnormally 

 large amounts of acetone cannot be demonstrated in the urine, and 

 is absent in many diseases in which a marked degree of acetonuria 

 exists. Normal urines, moreover, in which traces of acetone are 

 constantly found do not give the red color. At the present time we 

 are in total ignorance of the nature of the substance that is so com- 

 monly present in typhoid urines, and which reacts with diazo- 

 benzene- sulphonic acid in the manner indicated. 



Paralactic Acid. As I have shown, there is reason to believe 

 that the greater portion of the nitrogen which is set free in the 

 katabolism of the various tissues appears in the form of the am- 

 monium salt of paralactic acid and is transformed into urea in 

 the liver. Normally, indeed, paralactic acid is not found in the 

 urine. It occurs, however, whenever the further transformation of 

 the ammonium salt is impeded, and is hence met with in various 

 diseases of the liver which are associated with an extensive destruc- 

 tion of the hepatic parenchyma, as also in conditions in which the 

 oxidation-processes of the body are impaired in general. It is thus 

 notably met with in acute yellow atrophy, in poisoning with phos- 

 phorus and carbon monoxide, in long-continued anaemic conditions, 

 etc. (see also page 223). Smaller amounts have been found in 

 soldiers after forced marches, and in epileptic patients after severe 

 convulsive seizures. 



Isolation. To isolate the substance from the urine the following 

 method may be employed as suggested by Araki : 



The collected urine of twenty-four hours is evaporated to 



