752 UREA AND ITS ALLIES, [App. 



If the existence of some cyanogen residue is thus assumed in the 

 molecule of uric acid, then it must be supposed that before urea can be 

 obtained from it a molecular change takes place by which a portion at 

 least of the nitrogen of the uric acid is converted into the same condition 

 as the rest of the nitrogen, viz., into the amide state. 



If this be so, since the metabolism of the animals in which uric acid 

 replaces urea cannot be supposed to be fundamentally different from 

 that of the urea-producing animals, we may infer that the antecedent 

 of both uric acid and urea in the regressive metabolism of proteids 

 is, as we suggested above, a body containing some at least of its nitrogen 

 in the form of cyanogen 1 . 



Kreatin. C 4 H. N 3 O 2 . 



Occurs as a constant constituent of the juices of muscles, though 

 possibly it may be formed during the process of extraction by the 

 hydration of kreatinin. Kreatin is not a normal constituent of urine, 

 but it is said to occur in traces in several fluids of the body. When 

 found in urine its presence is probably due to the conversion of 

 kreatinin, a constant constituent of urine, into kreatin during its 

 extraction, since Dessaignes 3 has shewn that the more rapidly the 

 separation is effected, the less is the quantity of kreatin obtained, and 

 the greater the amount of kreatinin. 



In the anhydrous form it is white and opaque, but crystallises with 

 one molecule of water in colourless transparent rhombic prisms. It 

 possesses a somewhat bitter taste, is soluble in cold, extremely soluble in 

 hot water, is less soluble in absolute than in dilute alcohol, and is soluble 

 in aether. 



It is a very weak base, scarcely neutralising the weakest acids. It 

 forms crystalline compounds with sulphuric, hydrochloric and nitric 

 acids. 



Preparation. From extract of muscle by precipitating completely 

 with basic lead acetate, and crystallising out the kreatin, mixed with 

 kreatinin. From this latter it is separated by the formation of the 

 zinc-salt of kreatinin, kreatin not readily yielding a similar compound. 



Kreatin may be converted into kreatinin under the influence of acids, the trans- 

 formation being one of simple dehydration. 



Kreatin may be decomposed into sarcosin (methyl-glycin) and urea : 

 C 4 H 9 N 3 2 + H a O = C 3 H 7 N0 2 + CH 4 N 3 O ; 



1 See V. Knieriem, Zeitsch. f. Biol Bd. xm. (1877), S. 36. Schroder, Zeitsch. /. 

 Physiol. Chem. Bd. n. (1878), S. 228. 



2 J. Pharm. (3) Bd. xxxn. S. 41. 



