130 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



the sulphur, peculiar to certain families, all the members of 

 which excrete normally relatively large quantities of the sub- 

 stance (0.5-1.0 grm. for 24 hours). 



The appearance of the characteristic crystals and an 

 abnormal amount of lead-blackening sulphur in the urine 

 is sufficient proof of the presence of cystine. 



FATTY ACID DERIVATIVES. 



Associated with certain peculiar metabolic disturbances, 

 three closely related substances (/9-oxybutyric acid, diacetic 

 acid, and acetone) may appear in the urine either separately 

 or together. They have been noticed in severe cases of 

 diabetes, scarlet fever, cachexia, etc., and are the cause of 

 that aromatic fruity (apple-like) odor which is so frequently 

 present in diabetic urines. /3-oxybutyric acid only appears 

 in conjunction with acetone or diacetic acid, but the latter 

 two are often found alone in the urine. 



^-OXYBUTYRIC ACID, CH 3 -CH(OH) -C 



It is only necessary to test for this substance in urine 

 which contains diacetic acid. Since this body is Ia3vogyrate 

 and non-fermentable, the urine after fermentation should 

 turn the plane of polarized light to the left. This is not 

 sufficient evidence, however, since the conjugate glycuronates 

 also are Ia3vogyrate after fermentation. The following test 

 had better be added as confirmatory of #-oxy butyric acid. 



Evaporate some fermented urine to a syrup and after 

 the addition of an equal volume of concentrated H 2 S0 4 

 distil directly without cooling; a-crotonic acid CH 3 CH 



is formed and distils over, and the acid 



