EXCREMENTITIOUS SUBSTANCES. 89 



than the facts previously known appeared to justify. These substances are 

 termed Creatine and Creatinine^ designations which were conferred upon them 

 from their presence in the "juice of flesh/' of which they are constant constitu- 

 ents, and from which they may be most readily obtained. Creatine is a neutral 

 substance, presenting itself in the form of colorless transparent crystals, which, 

 when they are deposited from a concentrated solution, are long and acicular, 

 but when formed more slowly are short and thick ; these crystals contain two 

 equivs. of water of crystallization, which they lose when heated to 112, them- 

 selves becoming opaque. It is very soluble in hot water, but requires 74.4 

 parts of cold water to dissolve it. It is of a bitter, strongly pungent taste ; 

 and irritates the pharynx. Its formula is 80, 9H, 3N, 40. The proportion 

 which creatine bears to the whole mass of flesh is very small, and is subject to 

 considerable variation in different animals, as well as (probably) in different 

 states of the same. Thus in 1000 parts of ox-heart, Dr. Gregory found from 

 1.37 to 1.42 parts of creatine ; in the same amount of the flesh of the cod, 0.93 

 in one experiment, and 1.7 (or nearly double) in the other ; in the flesh of a 

 pigeon, 1.82 parts ; and in that of a skate no more than 0.60 parts. It has not 

 been detected in the substance either of the brain, liver, or kidneys ; and its 

 proportion in the urine is so small that this has not yet been determined, its 

 place being almost entirely occupied by creatinine. When creatine is boiled 

 with alkaline solutions or with baryta-water, it is resolved into Urea and a new 

 substance termed Sarcosine; and for the reasons already given ( 53), it seems 

 likely that some such change as that represented by the following formula takes 

 place in the living body : 



C. H. 0. N. C. H. 0. N. 



{2 4 2 2 = 1 equiv. Urea. 

 6714 = l "^ Cosine. 

 8 11 3 6 



It is true that Sarcosine does not make its appearance, as such, in the solids or 

 fluids of the body ; but there is reason to think that it may be rapidly decom- 

 posed, for, by the addition of one equiv. of water, it would become isomeric 

 with lactate of ammonia, and may not impossibly, therefore, be further reduced 

 by the respiratory process, in the same manner as are the lactates generally 

 ( 49). Although Creatine dissolves unchanged in dilute acids, it becomes con- 

 verted, by heating with strong acids, into Creatinine, giving off two equivs. of 

 water. This substance, which also forms prismatic crystals, moderately soluble 

 in water, differs considerably from creatine in its chemical relations ; for it has 

 a strong alkaline reaction, even separating ammonia from its salts, and serves as 

 a powerful base to acids, with which it forms soluble and readily crystallizable 

 salts. It also forms double salts with various metallic compounds, in a man- 

 ner very analogous to ammonia ; and among these is the white crystalline com- 

 pound with chloride of zinc, whose production in the urine, upon the addition of 

 that substance, first led to the detection of creatine and creatinine as consti- 

 tuents of the secretion. 



61. The relations of these two substances, both chemical and physiological, 

 pretty clearly indicate that Creatinine is to be regarded as a derivative from 

 Creatine ; for whilst the latter predominates in the juice of flesh, almost to the 

 exclusion of the former, the former predominates in the urine almost to the ex- 

 clusion of the latter. Moreover, as we have just seen, creatinine may be pro- 

 duced by a very simple process from creatine ; and this change takes place in 

 urine even after it has passed out of the body, for, when putrid, this fluid is no 

 longer found to contain creatine, the whole of that substance having undergone 

 metamorphosis. On the other hand, creatinine cannot be converted into crea- 



