280 THE URINE. 



On the other hand, it is known that an existing acetonuria can be 

 diminished or indeed suppressed by the administration of carbohy- 

 drates and that the elimination of carbohydrates from the diabetic's 

 diet often leads to acetonuria. A liberal administration of albumins 

 has in some cases the same effect upon the acetonuria as the carbo- 

 hydrates. These facts in turn could be interpreted as support- 

 ing the view regarding the derivation of oxybutyric acid from the 

 fats, both carbohydrates and albumins preventing the destruction of 

 fats. But, on the other hand, as has just been stated, the acetonuria 

 may be increased by the administration of fats in the absence of 

 carbohydrates. The entire question is thus still sub judice. 



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 Kulz reports that in three cases a daily elimination of 

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



The chemical relation which exists between /9-oxy butyric acid, 

 diacetic acid, and acetone is seen from the equations : 



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



/3-o xy butyric acid. Diacetic acid. 



(2) (CH 3 .CO)CH 2 .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 /?-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-crotonic acid. 



Test. As the presence of oxybutyric acid presupposes that of 

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

 readily be demonstrated than that of oxybutyric acid, a test in this 

 direction should always precede a more detailed examination (see 

 below). If a positive reaction is thus obtained, any sugar that may 

 be present is removed by fermentation. The liquid is cleared by 

 adding neutral acetate of lead, when the filtrate is examined with 

 the polarimeter. Should Isevorotation now be observed, the presence 

 of oxybutyric acid is rendered very probable. To demonstrate this 

 beyond a doubt, the liquid is evaporated to a syrup, treated with an 

 equal volume of concentrated sulphuric acid and distilled, without 

 cooling. In this manner the oxybutyric acid is decomposed with 

 the formation of a-crotonic acid, which is accordingly found in the 

 distillate. If this is present in larger amounts, it crystallizes out in 

 the distillate, when this is strongly cooled, and may be identified by 



