758 UREA AND ITS ALLIES. [APP. 



occurring as a constituent of any animal tissue or secretion. It is on the 

 other hand found normally in plants, notably in beet-sugar molasses. It 

 arises also as a constant product of the action of alkalis and other reagents 

 on both vegetable and animal proteids, and of acids on gelatine 1 . It thus 

 possesses considerable interest in respect of its relation to the proteids 

 (see p. 721). It crystallises in rhombic prisms which are but sparingly 

 soluble in cold water or alcohol, readily soluble in boiling water. Its 

 acid solutions are dextrorotatory, its alkaline laevorotatory and reduce 

 Fehling's fluid. It forms a characteristic readily crystallisable compound 

 with copper. Nitrous acid converts it into malic acid. 



Glutaminic acid. C 5 H 9 N0 4 . 



The circumstances and conditions under which this body occurs are 

 in general the same as for the aspartic acid, and hence as a product of 

 proteid decomposition it acquires some importance. It has not however 

 as yet been obtained by the action of pancreatic ferments on proteids 

 and in this it differs from the preceding body. 



It crystallises in rhombic tetrahedra or octahedra; is not very soluble 

 in cold, but readily soluble in hot water; insoluble in alcohol and 

 aether. Its acid solutions possess a strong dextrorotatory power and it 

 reduces Fehling's fluid. 



Cystin. C 3 H 7 NS0 2 . 



Is the chief constituent of a rarely occurring urinary calculus in men 

 and dogs. It may also occur in renal concretions, and in gravel, and is 

 occasionally found in urina 



From calculi it is obtained, by extraction with ammonia, as colour- 

 less six-sided tables or rhombohedra, which are neutral and tasteless. 

 It is insoluble in water, alcohol and aether, soluble in ammonia and the 

 other alkalis, and also in mineral acids. The fact that this body is one 

 of the few crystalline substances, occurring physiologically, which 

 contain sulphur, renders its detection very easy. Apart from its 

 insolubility in water, &c., it yields with caustic potash and salts of 

 either silver or lead, a brown colouration due to the presence of the 

 sulphides of these metals. 



According to Dewar and Gamgee 2 cystin is amido-sulpho-pyruvic acid, and its 

 formula is C 3 H 5 NS0 2 pyruvic being lactic acid minus two atoms of hydrogen. 



1 Horbaczewski, Sitxb. d. k. Akad. d. Wiss. Wien, 1890. 2 Abth. Juui-Heft. 

 a Journ. of Anat. and PJtysioL, Nov. 1S70, p. 143. 



