PROTEIDS. 



603 



It is a sulphur derivative of an amidolactic-acid, and has the 

 formula : 



CH 3 CH 3 



NH 2 C S S C NH 2 

 COOH COOH 



It may appear in small quantity in certain diseases, but is generally 

 a product of peculiar disordered metabolism, which is found to be char- 

 acteristic of certain families. Members of such families may excrete 

 habitually from O5 to 1 grin, daily. It sometimes separates as a crystal- 

 line deposit from the urine, and occasionally forms calculi in the urinary 

 tract. 



Physiologically it is of interest, in that cystine or substances allied to 

 it are probably the precursors of certain of the normal sulphur compounds 

 of the urine (p. 632). 1 



Its crystals are very characteristic, being usually in the form of 

 hexagonal plates (Fig. 55); more rarely it appears in rhombohedral 

 form. Urine which contains it will, if heated with caustic potash and 

 plumbic acetate, give a black precipitate of lead sulphide. 



PROTEIDS. 



Normal urine contains but traces of substances belonging or allied 

 to the proteid group. But minute quantities of a nucleo-proteid derived 

 from the cells of the urinary passages 

 are seldom or never absent. In the 

 majority of cases the amount of this 

 is so small that it is difficult directly 

 to demonstrate its presence. The 

 flocculent cloud which generally 

 separates on standing, even from the 

 clearest urine, by no means always 

 contains any isolated proteid, but may 

 consist entirely of intact epithelium 

 cells. But the nucleo-proteid may 

 be detected by suitable tests in the 

 precipitate which falls when large 

 quantities of normal urine are mixed 

 with alcohol. 



The nucleo-proteid may, on the 

 other hand, so far increase in con- 

 ditions of apparent health, that the urine will react to Heller's test 

 (vide infra). Thus Flensburg 2 found, on examining the urine of 1252 

 healthy persons, that 97 of these gave a reaction with nitric acid, which 

 could be shown to be due to a nucleo-proteid. 



In such cases, and in others where the increase is greater and due to 

 inflammatory changes in the urinary tract, the nucleo-proteid may be 

 precipitated by the addition to the urine of acetic acid in the cold; 

 especially if the fluid be first diluted to eliminate the solvent action of 



1 Goldmann and Baumann, ibid., 1888, Bd. xii. S. 254. 



2 Skandin. Arch. f. PhysioL, Leipzig, 1893, Bd. iv. S. 410. 



FIG. 55. Cystine. 



