AND OTHER URINARY DEPOSITS 155 



CYSTIN. 



Cases of cystinuria are not common. Sometimes 

 the deposit forms a yellowish-green waxy calculus ; 

 more often, flat hexagonal crystals are passed. 



In the chapter on the digestion and absorption of 

 proteins, it was explained that our modern conception 

 of the molecule is that of a long-linked chain of 

 aminoacids, grouped as monoamines, diamines, 

 and aromatic amines. The diamines ordinarily met 

 with in a protein digest are called arginin, lysin, 

 and ornithin. Of this group, cystin is a member, 

 though it is not always present amongst the 

 products of protein dissolution. Its formula is 

 diamino-/3-thiopropionic acid ; it therefore contains 

 the sulphur of the protein molecule. It has been 

 obtained from hair by chemical disintegration. 



It is suggested that in cases of cystinuria a physio- 

 logical ferment is lacking which should convert the 

 cystin into some simpler product. In a few of the 

 patients, other abnormal diamines, such as cadaverin, 

 have also been found in the urine ; in some cases 

 no abnormal amines except the cystin have been 

 detected. In a number of cases leucin and tyrosin 

 were being excreted as well. 



Variations in the diet influence but little the 

 output of cystin in a cystinuric. Feeding on 

 arginin (a diamine) or tyrosin (an aromatic amine) 

 makes no difference. Feeding on cystin itself merely 

 increases the output of sulphates. 



Cystin is soluble in ammonia. 



It will be observed that we cannot exercise any 

 useful control over the output of this deposit. It is 

 a life-long abnormality. 



