AND OTHER URINARY DEPOSITS 93 



taken sparingly. If he is obeying directions, a fresh 

 specimen of his urine, mixed with an equal amount 

 of spirit and allowed to stand, will deposit only a 

 few small crystals of oxalate, and a specimen without 

 the addition of spirit will show no crystals even on 

 centrifugalizing. Occasionally, however, one may 

 find a case in which oxaluria persists even on a milk 

 diet. We must then restrict the sugars and starches 

 of the diet, and give remedies calculated to diminish 

 fermentation in the stomach and intestines. 



If patients object to dietetic restrictions, potassium 

 citrate will often relieve, both by acting as a diuretic, 

 and by making the urine alkaline, thus dissolving 

 the crystals. 



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, 

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

 member, though it is not ordinarily 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 



