274 Tin-: VRL\E. 



ence will scarcely be suspected. If, however, a urine develops a 

 marked odor of hydrogen sulphide on standing, it is well to add an 

 excess of acetic acid and to examine the sediment somewhat later. 

 The characteristic hexagonal platelets of eystin may then at times 

 be found, and can be recognized from their solubility in ammonia 

 and hydrochloric acid, while they are insoluble in acetic acid, 

 water, alcohol, and ether. But sometimes this procedure does not 

 lead to the desired end, even though a decided increase in the 

 amount of neutral sulphur is observed, and hydrogen sulphide is 

 formed in abundance on standing. Whether or not it may then 

 be justifiable to refer this increase of the neutral sulphur to the 

 presence of eystin, is questionable. 



Clinically eystin is of interest in so far as its continued appear- 

 ance in the urine may be regarded as a probable precursor of the 

 formation of eystin gravel or calculi ; and we find, as a matter of 

 fact, that this occurs in a very considerable proportion of all cases. 



A quantitative estimation of the eystin, isolated as such, is not as 

 yet possible. When it is found in a sediment the crystals may be col- 

 lected and weighed. But as a variable amount remains in solution, 

 even after the addition of much acetic acid to the urine, it is further 

 necessary to estimate the total amount of neutral sulphur that re- 

 mains, when an excess beyond the average figures may be referred to 

 oystin, and the result added to that obtained directly. 



Isolation. As the synthesis of eystin has not as yet been effected, 

 we are generally obliged to rely upon eystin concretions for purposes 

 of study. If such material is inaccessible, we may prepare the sub- 

 stance from horn shavings by decomposing the contained keratins 

 with mineral acids. For the isolation of the body from the result- 

 ing decomposition -products, however, I must refer the reader to 

 Morner's article. 



Properties. Several varieties of eystin apparently exist, of which 

 one is laevorotatory, another dextrorotatory, while a third is optically 

 inactive. The common eystin which is found in the urine belongs 

 to the Isevorotatory type. It crystallizes in colorless, hexagonal 

 platelets, which are quite characteristic. They are soluble in solu- 

 tions of the alkaline hydrates, in ammonia, and the mineral acids. 

 In water, alcohol, ether, and acetic acid the substance is insoluble, 

 as also in solutions of ammonium carbonate, and it is for this 

 reason that eystin is apt to crystallize out from decomposing urines 

 if it was previously present in solution only. 



Structurally, eystin is the disulphide of cystei'n, which in turn is 

 tf-amido-thiolactic acid. On reduction it is transformed into cystei'n, 

 as shown in the equation : 



CH, CH 3 CH 3 



| >H 2 NH 2X j NH 2X I 



r/ >C + 2H=2 /C 



! S SK | SH / I 



COOH COOH COOH 



Cystin. Cystein. 



