114 PHYSIOLOGICAL CHEMISTRY. 



cular tissue, both voluntary and involuntary, of man and animals ; its 

 proportion in human muscles being, according to Neubauer,* about 

 two parts per thousand. It has also been found in minute quantity in 

 the blood, the brain, and the kidneys. It is soluble in cold, very readily 

 in hot water, slightly soluble in alcohol, insoluble in ether. From its 

 watery solution it crystallizes in transparent, colorless, rhombic prisms 

 of firm consistency. It is decomposed by a temperature of 100 C. 

 By boiling in acid solutions, or by long-continued boiling in water, it 

 is transformed into another closely related substance, namely, creati- 

 nine. If boiled with baryta- water it produces, among other substances, 

 urea, carbonic acid, and ammonia. Creatine is regarded as a product 

 of the metamorphosis of albuminous matters, especially of those exist- 

 ing in muscular tissue. It does not appear in the urine, but undergoes 

 a further transformation, probably into the following substance. 



8. Creatinine, C 4 H 7 N 3 0, 



Is known to exist, with certainty, only in the urine. Although occa- 

 sionally found in the muscles, it is generally regarded by physiological 

 chemists (Neubauer, Hoppe-Seyler, Gorup-Besanez), not as a normal 

 ingredient of the muscular tissue, but as a product of transformation 

 of the previously existing creatine. It is soluble in water and in 

 alcohol, but only slightly soluble in ether. It crystallizes in colorless, 

 glittering prisms. In solution it has a strongly alkaline reaction, 

 decomposes the combinations of ammonia, and forms with various 

 acids neutral salts. 



The chemical relation between these two bodies is such that by 

 hydration or dehydration they may be converted into each other. In 

 the interior of the body creatine is no doubt converted into croatinine, 

 since the former 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 = CJI 7 N 3 0. 



Creatine thus represents an intermediate stage of metamorphosis, and 

 finally appears in the urine under the form of creatinine. According 

 to Neubauer, the quantity of creatinine discharged by a healthy man, 

 under ordinary diet, is about one gramme per day. 



9. Urea, CH 4 N 2 0. 



This, the most important and well known substance of its class, is 

 the principal solid ingredient of the urine, and the main product of the 

 decomposition of nitrogenous matters in the body. It is most abun- 

 dant 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 amounts to 

 only 0.16 part per thousand. As it makes its appearance in the blood, 

 it is drained away by the kidneys, and thus accumulates in larger 



* Neubauer und Vogel, Analyze des Harns. Wiesbaden, 1872, p. 20. 



