554 THE URINE. [CH. xxxvn. 



This was known before, so the chief interest centres round two 

 new substances, precipitable by phosphotungstic acid. One of 

 these is called lysine (C6H 14 N 2 2 , probably di-amido-caproic 

 acid) ; the other was first called lysatinine. Hedin then showed 

 that lysatinine is a mixture of lysine with another base called 

 arginine (C 6 H 14 N 4 2 ) ; it is from the arginine that the urea comes 

 in the experiment to be next described. Arguing from some 

 resemblances between this substance and creatinine, Drechsel 

 expected to be able to obtain urea from it, and his expectation 

 was confirmed by experiment. He took a silver compound of 

 the base, boiled it with barium carbonate, and after twenty-five 

 minutes' boiling obtained urea. 



It is, however, extremely doubtful whether the chemical decom- 

 positions produced in laboratory experiments on proteids are 

 comparable to those occurring in the body. Many physiologists 

 consider that the amido-acids are intermediate stages in the meta- 

 bolic processes that lead to the formation of urea from proteids. 

 We have already alluded to this question in relation to the creatine 

 of muscle, and we are confronted with the difficulty that injection 

 of creatine into the blood leads to an increase not of urea, but of 

 creatinine in the urine. If creatine is an intermediate step, it must 

 undergo some further change before it leaves the muscle. Other 

 amido-acids, such as glycocine (amido-acetic acid), leucine (amido- 

 caproic acid) and arginine are probably to be included in the 

 same category ; there is, however, no evidence that tyrosine acts 

 in this way. The facts upon which such a theory depends are 

 (i) that the introduction of glycocine or leucine into the bowel, 

 or into the circulation, leads to an increase of urea in the urine ; 

 and (2) that amido-acids appear in the urine of patients suffering 

 from acute yellow atrophy of the liver. Then, again, it is per- 

 fectly true that, in the laboratory, urea can be obtained from 

 creatine, and also from uric acid, but such experiments do not 

 prove that creatine or uric acid are normally intermediate pro- 

 ducts of urea formation in the body. Still, if we admit for the 

 sake of argument that amido-acids are normally intermediate 

 stages in proteid metabolism, and glance at their formulae 



Glycocine, C 2 H 5 N02, 

 Leucine, C 6 H 13 N02, 

 Creatine, C 4 H 9 N 3 2 , 



we see that the carbon atoms are more numerous than the 

 nitrogen atoms. In urea, CON 2 H 4 , the reverse is the case. The 

 amido-acids must therefore be split into simpler compounds, 

 which unite with one another to form urea. Urea formation 



