94 THE PHYSIOLOGY OF URIC ACID 



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. 



GENERAL LAWS OF CALCULUS FORMATION. 



When the chemist sets aside a fluid to crystallize 

 out, he does not obtain a single rounded mass of 

 concentric layers, but many hundreds of separate 

 crystals, some large, some small, each with its 

 characteristic symmetry. The same is generally 

 true in the bladder, and separate crystals, of oxalate, 

 phosphate, or uric acid, are commonly passed. Yet 

 in certain circumstances a totally different picture 

 is obtained, and a calculus forms, with its micro- 

 crystalline structure, its concentric layers, and its 

 nucleus. What determines the difference ? 



The geologist is confronted with the same problem. 

 Spherical concretions, whose structure is essentially 

 similar to that of urinary calculi, are repeatedly met 

 with in Nature. They may be composed of carbonate 

 of lime, of silica, or of any of a score of other chemical 



