URINE 113 



ducing urea from casein. More recent work has shown that this is 

 true for other proteids also. If a proteid is decomposed by hydro- 

 chloric acid, a little stannous chloride being added to prevent oxida- 

 tion, a number of products are obtained, such as ammonium salts, 

 leucine, tyrosine, aspartic and glutaminic acids. This was known 

 before, so the chief interest centres round two new substances, 

 precipitable by phosphotungstic acid. One of these is called lysine 

 (C^Hi4N20.2, probably di-amido-caproic acid) ; the other was first 

 called lysatinhic. Hedin then showed that lysatinine is a mixture of 

 lysine with another base called arginine (C6H,4N402) ; it is from the 

 arginine that the urea comes in the experiment to be next described. 

 Arguing from some resemblances between this substance and creatine, 

 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 m-ea. Drechsel's comparison of arginine to creatine 

 has turned out to be correct; on decomposition it breaks up into 

 di-amido-valerianic acid and cyanamide (CN.NHj) from which the 

 urea originates. (Schulze and Winterstein.) Lysine and arginine 

 are two of the hexone bases (see p. 32). 



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

 positions produced in laboratory experiments on proteids are com- 

 parable with those occumng in the body. Many physiologists consider 

 that the amido-acids are intermediate stages in the metabolic pro- 

 cesses 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 difl&culty 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) and leucine (amido-caproic acid) and 

 arginine, are to be included in the same categor}-. The facts upon 

 which such a theory depends are (1) that the introduction of glycocine 

 or leucine into the bowel, or into the circulation, leads to an increase of 

 urea in the urine ; there is, however, no evidence that t^Tosine acts in 

 this way ; and (2) that amido-acids appear in the urine of patients 

 suffering from acute yellow atrophy of the liver. Then again it is 

 perfectly 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 is a normally intermediate product of urea 

 formation in the body. Still, if we admit for the sake of argument 



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