EXCREMENTITIOUS SUBSTANCES. 93 



weak solution of carbonate of' potass, which dissolves uric acid. 1 It is soluble, 

 however, in the fixed alkalies and ammonia, as also in nitric and sulphuric 

 acids. As no compounds have yet been obtained, by which its combining 

 equivalent can be determined, the formula 50, 211, 2N, 20, must be con- 

 sidered as representing nothing more than the percentage composition of its 

 elements ; and, although this only differs from that of hydrated Uric acid in the 

 want of a single equiv. of oxygen, yet all attempts to generate either from the 

 other, or to obtain urea from uric oxide, have hitherto failed. So, also, it seems 

 to differ from Hypoxanthine ( 57) only in containing one more equiv. of oxy- 

 gen ; but no real relation has been shown to exist between these substances. 

 Of the conditions under which Xanthine is formed in the living body, it is im- 

 possible at present to form the slightest idea. Strahl and Lieberkiihn believe 

 that they have discovered it in ordinary Human urine ; but the substance which 

 they describe seems rather to be Guanine ( 57, note), which, when first dis- 

 covered, was mistaken for Xanthine, but which differs from it in composition 

 and properties, and is readily distinguished from it by its solubility and hydro- 

 chloric acid. Guanine is a yellowish-white crystalline powder, devoid of odor 

 or taste, insoluble in water, and having no action on vegetable colors; it serves, 

 however, as a base to acids, though its salts are very unstable ; and its formula 

 is IOC, 5H, 5N, 20+ HO. Guanine appears, from the researches of Will 

 and Gorup-Besanez, 3 to be one of the characteristic constituents of the urinary 

 secretion in Invertebrated animals ; and, if it should prove to be of constant 

 or even of frequent occurrence in Human urine, the fact will be one of no 

 little interest. No doubt can be entertained, that Xanthine and Guanine are 

 both of them to be regarded as products of the metamorphosis of the azotized 

 tissues. 



66. A substance is occasionally found in Urinary calculi, and also in sedi- 

 mentary deposits, which is remarkable for the large proportion of Sulphur 

 amounting to 26.66 per cent. included in its composition. The substance, 

 termed Cystine, occurs in the form of colorless, transparent, hexagonal plates or 

 prisms, is devoid of taste or smell, is insoluble in water and alcohol, and has no 

 action on vegetable colors ; but it serves as a base to oxalic and the mineral 

 acids, forming with them saline combinations, most of which are crystallizable. 

 Its formula is 6C, 6H, IN, 2S, 40 ; but no probable account can yet be 

 given of the mode in which these equivalents are combined and arranged. It 

 is very readily soluble in ammonia, but forms no compound with it, so that on 

 the evaporation of the ammonia it crystallizes in its characteristic tablets; and 

 by this character, as well as by the peculiar and disagreeable odor which it 

 emits in burning when heated on platina-foil, cystine may be readily distin- 

 guished from any other urinary sediment. Though its occasional presence in 

 urine has not been noticed by many observers, yet it would appear sometimes 

 to exist there in considerable quantity, forming a nearly white or pale fkwn- 

 colored pulverulent deposit, much resembling the pale variety of urate of am- 

 monia, for which it is liable to be mistaken ; and so copious may this be, that 

 Dr. G. Bird states that he has seen a 6 oz. bottle full of urine let fall by repose 

 a sediment of cystine to the depth of half an inch. According to this excellent 

 observer, the presence of cystine in the urine may often be detected by micro- 

 scopic examination, where it forms no distinct deposit ; and this especially in 

 strumous subjects, a class which he regards as peculiarly subject to cystin-urea. 

 It has also been observed in chlorotic subjects. There can be no doubt that 

 cystine is one of the forms under which the products of the metamorphosis of 

 the albuminous tissues present themselves ; and its composition is not so far 



1 See Dr. Golding Bird's "Urinary Deposits," pp. 138-142, Am. Ed. 



2 "Ann, der Chem. u. Pharm.," band Ixix. p. 117. 



