COMPOSITION OF THE URINE. 



419 



generally regarded as excrementitious matters, taken from the tissues by the blood, to be 

 eliminated by the kidneys. 



Creatine has a bitter taste, is quite soluble in cold water (one part in seventy-five), and 

 is much more soluble in hot water, from which it separates in a crystalline form on cool- 

 ing. It is but slightly soluble in alcohol and is insoluble in ether. A watery solution 

 of creatine is neutral. It does not readily form combinations as a base ; but it has lately 

 been made to form crystalline compounds with some of the strong mineral acids, the 

 nitric, hydrochloric, and sulphuric. When boiled for a long time with baryta, it is changed 

 into urea and sarcosine ; but the recent researches of Voit have pretty conclusively shown 

 that this change does not take place in the living organism, and that probably none of the 

 urea of the urine is produced in this way. When boiled with the strong acids, creatine 

 loses four atoms of water and is converted into creatinine. This change takes place very 

 readily in decomposing urine, which contains neither urea nor creatine but a large quan- 

 tity of creatinine, when far advanced in putrefaction. 



Fi<;. 122. Creatine, extracted from the, muscular 

 tissue, and crystallized from a hot, watery 

 solution. (Funke.) 



FIG. 128. Creatinine, formed from creatine by 

 digestion with hydrochloric acid, and crystal- 

 lised from a hot, watery solution. (Funke.) 



Creatinine is more soluble than creatine, and its watery solution has a strongly alka- 

 line reaction. It is dissolved by eleven parts of cold water and is even more soluble in 

 boiling water. It is slightly soluble in ether and is dissolved by one hundred parts of 

 alcohol. This substance is regarded as one of the most powerful of the organic bases, 

 readily forming crystalline combinations with a number of acids. According to Thudi- 

 chum, who has very closely studied the physiological relations of these substances, crea- 

 tine is the original excrementitious principle produced in the muscular substance, and 

 creatinine is formed in the blood by a transformation of a portion of the creatine, some- 

 where between the muscles and the kidneys ; " for, in the muscle, creatine has by far the 

 preponderance over creatinine ; in the urine, creatinine over creatine." 



In the present state of our knowledge, there is very little to be said with regard to 

 the physiological relations of creatine and creatinine, except that they are probably to be 

 classed among the excrementitious principles resulting from the disassimilation of the 

 muscular tissue. As they exist in considerable quantity in the muscular substance, it be- 

 comes a question whether, in the urine of carnivorous animals, they be not derived from 

 the food ; but they could have no such origin in the herbivora or in the urine of starving 

 animals. 



It has been assumed by many authors that, inasmuch as the muscular tissue of the 

 heart is in almost constant action, it should contain more creatine than any other portion 

 of the muscular system ; but late observations on this point show that the reverse of this 



