598 THE CHEMISTRY OF THE URINE. 
procedure is our most convenient method for following the variations in the 
excretion of the xanthin group. 1 
Tests. — Xanthin and its two homologues, and also carnin, but not the 
other bases, give WeideVs reaction. This is almost identical with the 
murexide test described for uric acid, but chlorine water is used instead 
of nitric acid. The bases resist oxidation with nitric acid much more 
fully than does uric acid, but, in the presence of a small quantity of a 
chloride, xanthin will give the ordinary murexide reaction. Very 
characteristic of xanthin and hypoxanthin are the crystalline precipi- 
tates which they yield with silver nitrate in the presence of nitric 
acid. 
Variations in the amount of the urinary xanthin bases closely follow 
those of uric acid, and for the most part depend upon the same 
influences. The bases, however, are apt to vary even more widely. 
According to Camerer 2 they are greatly increased by certain forms of 
vegetable food ; thus, in one experiment, on a flesh diet the nitrogen 
present as these bases was only O'l per cent, of the total nitrogen ; 
while, when green vegetables formed the chief ingredient of the food, it 
was - 6 per cent. They are increased by diet rich in nucleins, 3 and. 
pathologically their amount is greatly raised in some forms of leukaemia. 
(f) Creatinin. — This base is chemically distinct from the alloxuric 
compounds, in that its molecule contains neither the alloxan ring nor 
the urea residues which are characteristic of these. Nevertheless, on 
hydrolysis, it easily yields urea and an amido-acid (methylglycine). It 
is the anhydride of creatin, which is itself methylglycocyamin. 
,NH, y NH 
C(NH}/ C(NH)< 
\N(CH 3 )-CH-COOH \N(CH 3 )-CH-CO 
(creatin) (creatinin) 
Whether creatin itself is ever a urinary constituent is somewhat 
uncertain. It has been stated to occur when the urine is excreted in 
alkaline condition, 4 but the quantity is, in any case, very small. So 
easily are the two substances converted the one into the other, that care 
is requisite in the isolation of either. When creatin stands in acid solu- 
tion, it tends to change into its anhydride, while creatinin in alkaline 
solution suffers the inverse change. 
G. S. Johnson 5 lias found, however, that urinary creatinin is not 
identical, but isomeric, with that obtained artificially from creatin {e.g. 
by the action of acids), and distinct from the creatinin found in small 
quantity in muscles. 
The creatinin of mine was first isolated by Liebig. It is present on 
an average to the extent of about I/O grin, in the excretion of twenty- 
four hours, when a mixed diet is taken. 
Properties. — In its compounds creatinin exhibits well-marked basic 
tendencies, and it can liberate ammonia from ammonium salts on boil- 
ing ; but, according to Salkowski, solutions of the pure substance react 
1 For details see Kriiger and "Wulff, loc. cit. supra. 
- Ztsclir.f. Biol., Miinchen, 1891, Bd. xxviii. S. 72. 
3 Weintrauil, loc. fit. 
4 Hoflemanii, Virchow's Arehiv, 1S69, Bd. xlviii. S. 35S. 
5 Proc. Hoy. Soc. London, 1S92, vol 1. p. 287. 
