URINE 129 



this for the spectroscope. Upon the addition of a small 

 amount of water the alcoholic extract will exhibit a red 

 fluorescence. For tests see under Blood, p. 78. 



CH 2 -S S-CH 2 



CYSTINE, CH-NH 2 CH-NH,. 



This substance has come into prominence of late as a 

 protein decomposition product containing sulphur in the 

 neutral or lead-blackening form. In fact, the cystine which 

 can be obtained in the decomposition of certain proteins 

 contains an amount of lead-blackening sulphur which corre- 

 sponds closely to the total sulphur of the original protein 

 molecule. This would seem to imply that the sulphur of 

 some proteins was present in the molecule as a cystine 

 nucleus, and that proteins containing large amounts of 

 neutral sulphur have present large numbers of cystine groups 

 in the molecule. Cystine is also closely related to Taurine, 



CH 2 .S0 3 H 

 NH 2 



^A-^^ 



t. 



a substance which contains oxidized sulphur in organic form 

 and which probably represents an intermediate stage of 

 oxidation between the neutral sulphur atom of cystine and 

 the mineral sulphates of the urine. Cystine, upon standing, 

 separates out of the urine as colorless six-sided plates, insolu- 

 ble in water, acetic acid, alcohol, and ether. It sometimes is 

 found in the form of calculi. Cystineuria has repeatedly 

 been observed as an apparently anomalous metabolism of 



