THE AROMATIC OXY- ACIDS. 265 



/9-Oxybutyric Acid. This acid is never found in the urine under 

 normal conditions, and is principally met with in the severer forms 

 of diabetes, when it is associated with the presence of diacetic 

 acid and acetone. It is supposedly derived from the albumins of 

 the tissues, and may accordingly also appear in the urine in various 

 cachectic conditions, in the continued fevers, and during starvation. 

 As a general rule it is found in combination with the common alkalies 

 of the blood, but when it is produced in especially large amounts a 

 corresponding quantity of ammonia is furnished by the body to effect 

 its neutralization. It may happen, however, that the acid formation 

 exceeds that of ammonia, and in such cases the free acid occurs in 

 the urime, and can also be demonstrated in the blood as such. 

 Symptoms of acid intoxication then exist, and it is noteworthy that 

 in such cases the amount of carbonic acid in the blood has been 

 found markedly diminished, showing that the alkaline salts are not 

 present in sufficient amount to remove the carbonic acid from the 

 tissues. 



Of the immediate antecedents of the acid nothing is known, and 

 if formed at all under normal conditions it is manifestly oxidized at 

 once beyond the stage of diacetic acid, as this substance also is only 

 found under pathological conditions. Traces of acetone, however, 

 which is likewise derived from oxy butyric acid, are found in every 

 urine. 



The amount of oxybutyric acid which may occur in the urine is 

 extremely variable. In the milder cases of diabetes it is usually 

 absent ; in the severer forms, however, large quantities may be 

 found, and Kiilz reports that in three cases a daily elimination of 

 67, 100, and 226 grammes, respectively, was observed. 



The chemical relation which exists between /3-oxybutyric acid, 

 diacetic acid, and acetone is seen from the equations : 



(1) CH 3 .CH(OH).CH 2 .COOH -f O = (CH 3 CO).CH 2 .COOH + H 2 O. 



/3-oxybutyric acid. Diacetic acid. 



(2) (CH 3 .CO)CH,.COOH = CO(CH 3 ) 2 + CO 2 . 



Diacetic acid. Acetone. 



We can thus readily understand that in certain conditions acetone 

 may be found in the urine alone, while in others diacetic acid, and 

 in still others /9-oxybutyric acid may be present as well. 



On boiling /9-oxybutyric acid in aqueous solution with dilute 

 mineral acids, a-crotonic acid results, and it is thus apparent that 

 this acid is also found in the distillate, when urine containing the 

 first is distilled with sulphuric acid. Otherwise, however, it does 

 not occur. The reaction which takes place may be represented by 

 the equation : 



CH 3 .CH(OH).CH 2 .COOH = CH 3 .CH==CHCOOH + H 2 O 



/3-oxybutyric acid. a-c-rotontic acid. 



Test. As the presence of oxybutyric acid presupposes that of 

 diacetic acid, and as the presence of the latter can much more 

 readilv be demonstrated than that of oxvlmtvric acid, a test in this 



