CHEMICAL BASIS OF THK ANIMAL BODY. 177 



vi. The compound of xanthin with hydrochloric acid is far 

 less soluble in water than are tin- similar compounds of hyjtuxan- 

 thin and guanin, and hence affords a further means of separating 

 tin -so bases. 



Hy treatment with hydro< -hloric acid and potassium chlorate 

 xanthin is converted into alloxan and urea (Fischer). 



Tin- older and frequently ivjieated >tatement> that xuntliin ami 

 hypo xanthin can In- obtained from uric arid \>\ tin- art ion of sodiuni- 

 ainali^alu, as also that hTpOXUltluO can he converted into xanthin by 

 treat inent with nitric acid, have recently Keen shown to he erroneous. 

 Notwithstanding the similarity of their composition these three sub- 

 stanco are incapable of interconversion. 1 



L'. Heteroxanthin. r II, N 4 < >, (M.-thyl-xanthin?). 



This substance occurs in minute quantities in the normal urine 

 of man- and the dog, 3 along with xanthin and hypoxanthin and 

 another closely allied xanthin-base, paraxanthin. It occurs in 

 larger amount in the urine of leukhaemic patients. It is crystal- 

 line, hut not very characteristically so, is soluble with difficulty 

 in (old water, much more soluble in hot water, is insoluble in 

 alcohol ami in ether. It may, as also may paraxanthin, be separated 

 from other xanthin-bases by taking advantage of the relatively 

 slight solubility of it< sodium salt in caustic soda. It also yields 

 with hydrochloric acid a relatively insoluble salt which crystal- 

 lises readily, whereas the corresponding salt of paraxanthin is 

 readily soluble. They may by this means be separated the one 

 from tin- other. 



Il-'teroxanthin does not give the ordinary reaction for xanthin 

 with nitric acid and caustic soda, but yields a brilliant colouration 

 on the application of Weidel's test (see sub xanthin). Like the 

 otln-i xanthin-bases it gives an insoluble salt with an ammoniacal 

 solution of nitrate of silver. 



Paraxanthin. C 7 H 8 N 4 2 (I)imethylxanthin ?) Isonieride of 



Theoliromin. 



Like heteroxanthin it oc.-ur- in very small amounts in urine. 1 

 It i- Miluble with difliculty in cold water, but is more soluble 

 than xanthin ; is much more soluble in hot water, insoluble in 

 alcohol and in ether. It crystallises readily in characteristic tlat. 

 somewhat irregular, six-sided tables when its solutions are slowly 

 evaporated, or in needles if rapidly. It forms, as do the preceding 



1 Iv ,,1,,/g,;,!. Ch.m. H.I. vi. (IHS2), S. 4-.'s Fis.h.T. 11. r d. d. chen. 



Gf> 



i---.. s :u>: 



in..,,, '/j , ' .,. H.|. M (!.:), S. 412. 



4 Tlm.li.-lmm. '.!fin/. nf rh. Ml. V..1 i ID..II, /trr. ,1. d 



s. i-.i:,. issr,, .-HIM;. '/.>. /: k-im. M*-<i. H.I. MI. (Suppl.-IIft.) (1884), 



{ >hy$iol. Cl il-'-'l). S. 319. 



12 



