CHEMICAL 11ASIS OF TIIK ANIMAL BODY. 173 



Preparation. Allantoiu may ! ea-ily obtain. -d l.y tin.- careful 

 oxidation of uric acid with pota-sium permanganate. 1 It may 

 also In- syntht-ti.M'd by prolonged heating to 100 of a mixture of 

 idyoxylic aciil and urea, 2 or of the latter substam-e with mooxalic 

 acid. 8 



As prepared artificially it crystalli>e> readily in large, pri-maiic 

 hexagonal crystals. 



FIG. 22. CRYSTALS OF ALLANTOIN I-I:I.I-M:I u BY THE OXIDATION 

 OF UKIC Ann. (After Kiihne.) 



In addition to the crystalline form and precipitability with 

 nitrates of mercury and silver, allantojn is further chnrart 

 by yielding Schiff s reaction with furf urol (see above, p. 1 58, sub 

 urea), but less readily and with less intense colouration than does 

 urea. It also reduces Fehling's fluid on prolonged lioiliim. 



THE XANTHIN GROIT.' 



This -jronp comprises a number of substances closely related t<> 

 uri'e a<-id ami to each other. Some of them occur in small annumis 

 in the tissues (muscles) and excretions (urine) of the body and are 

 to he regarded as being, like urea and urie acid, typical products 

 of the downward destructive metabolism <>f pmteids. Some of 

 t luMii are closi-ly n-laied to certain alkaloids which occur in plants 

 (thi-obromin and call'ein ), and which jirobably play some not unim- 

 p-irtant part in the nutritional changes of the animal body, sine.- 

 they an- constantly consumed, in sonic form or other, by the ! 

 part of the human race. This relationship ,,f tin- xanthin-bodies 

 Stable alkaloids is further interesting when it is 



| ( -liui-, /;,,-. >i. ,i. ,-ifm. <;. </;. IM MI i- 



mnaiix, Cnmjit. /innl. T. s.'t (ISTf,), ji. 62. 



Ch,m. JI. Vol. I 



4 l-'..r ,i full *trit'ini-iit nf tin- t."'ii'Tal n-:u -tinim of thin croup, and the metlioda for 

 thoir so|tarnti<>ii ami .ii-. riiainatiou, ee Neubaucr U. Vogei, Anaiyte drt Hants, 

 1890. Sec. 20O 219. 



