P ROTE IDS. 
60 - 
It is a sulphur derivative of an amidolactic-acid, and has the 
formula : 
CH 3 CH 3 
I I 
NH 2 — C— S— S— C— NH 2 
"I I 
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 0'5 to 1 grm. 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. 
Peoteids. 
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 suit aide tests in the 
precipitate which falls when large 
quantities of normal mine 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 nucleorproteid 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., 1S88, Bd. xii. S. 254. 
2 Skandin. Arch. f. Physiol., Leipzig, 1893, Bd. iv. S. 410. 
Fig. 55. — Cystine. 
