108 CKYSTALLIZABLE NITROGENOUS MATTERS. 



the change which takes place is undoubtedly the conversion of creatine 

 into creatinine, since the former is that which exists normally in the 

 muscles, while the latter is an ingredient of the urine. In this change 

 the elements of water are eliminated as follows : 



Creatine. Creatinine. 



C 4 H 9 N 3 2 H 2 = C 4 H 7 N 3 0. 



Thus creatine represents an intermediate stage of the products of meta- 

 morphosis, which finally appear in the urine under the form of creatinine. 

 According to the observations of Neubauer, the quantity of creatinine 

 discharged by a healthy man, under ordinary diet, is about 1 gramme 

 per day. 



Urea, CH 4 N 2 0. 



This is one of the most important and well known substances of its 

 class, as it is the principal solid ingredient of the urine, and the main 

 product of the decomposition of nitrogenous matters in the body. It is 

 most abundantly found in the urine, where it is present on the average, 

 in man, in the proportion of 26 parts per thousand ; while in the blood 

 it is only in the proportion of 0.16 part per thousand. As it makes its 

 appearance in the blood, it is constantly drained away by the kidneys, 

 and thus accumulates in larger proportion in the urine. This is further 

 shown by the comparative analyses of Picard, who found, in the dog, 

 the proportion of urea in the blood of the renal arteries to be 0.36 per 

 thousand, in the renal veins 0.18 per thousand. Urea has also been 

 found in minute quantity in the lymph, the aqueous and vitreous humors 

 of the eye, the crystalline lens, and the perspiration. 



Urea is a colorless, neutral substance, abundantly soluble in water 

 and in boiling alcohol, less so in cold alcohol, nearly insoluble in ether. 

 It crystallizes in four-sided prisms, often with blunt pyramidal ends, 

 which are decomposed on being heated above 120 (248 F.). Its pure 

 watery solution may be kept without change at ordinary temperatures ; 

 but by long continued boiling, or by a short boiling in the presence of 

 alkalies, it is decomposed with the production of ammonium carbonate. 

 If heated with water in an hermetically sealed tube to 180 (356 F.), 

 it undergoes the same alteration. This change takes place with the 

 assumption of the elements of water, as follows : 



Urea. Ammonium carbonate. 



CH 4 N 2 + HA (NH 4 ) 2 C0 3 . 



Urea has been produced artificially from albuminous matter, by 

 placing the latter in contact with potassium permanganate in watery 

 solution, and subjecting it to a heat of 60 to 80 (14(P to 176Q F.). 

 This reaction, first established by Bdchamp, 1 has been confirmed by 

 Hitter, 2 in whose experiments 30 grammes of albumen furnished 0.09 

 gramme of urea, and the same quantity of fibrine, 0.0 T gramme; 



1 Coraptes Kendus de I'AcadSmie des Sciences, Paris, 1870, tome Ixx. p. 866. 



2 Comptes Rendus, 1871, Ixxiii. p. 1219. 



