GENERAL CHARACTERS OF THE URINE. 349 



carbon are daily expelled from the body, is one of these substances ; 

 the others are urea, creatine, creatinine, and the urates. 



We see, then, in what way the organic matters, in ceasing to form 

 a part of the living body, lose their characteristic properties, and 

 are converted into cry stall! zable substances, of definite chemical 

 composition. It is a kind of retrograde metamorphosis, by which 

 they return more or less to the condition of ordinary inorganic 

 materials. These excrementitious matters are themselves decom- 

 posed, after being expelled from the body, under the influence of 

 the atmospheric air and moisture ; so that the decomposition and 

 destruction of the organic substances are at last complete. 



It will be seen, consequently, that the urine has a character 

 altogether peculiar, and one which distinguishes it completely 

 from every other animal fluid. All the others are either nutritive 

 fluids, like the blood and milk, or are destined, like the secretions 

 generally, to take some direct and essential part in the vital opera- 

 tions. Many of them, like the gastric and pancreatic juices, are 

 reabsorbed after they have done their work, and again enter the 

 current of the circulation. But the urine is merely a solution of 

 excrementitious substances. Its materials exist beforehand in the 

 circulation, and are simply drained away by the kidneys from 

 the blood. There is a wide difference, accordingly, between the 

 action of the kidneys and that of the true glandular organs, in 

 which certain new and peculiar substances are produced by the 

 action of the glandular tissue. The kidneys, on the contrary, do 

 not secrete anything, properly speaking, and are not, therefore, 

 glands. In their mode of action, so far as regards the excretory 

 function, they have more resemblance to the lungs than to any 

 other of the internal organs. But this resemblance is not complete ; 

 since the lungs perform a double function, absorbing oxygen at the 

 same time that they exhale carbonic acid. The kidneys alone are 

 purely excretory in their office. The urine is not intended to 

 fulfil any function, mechanical, chemical, or otherwise ; but is des- 

 tined only to be eliminated and expelled. Since it possesses PO 

 peculiar and important a character, it will require to be carefully 

 studied in detail. 



The urine is a clear, watery, amber-colored fluid, with a distinct 

 acid reaction. It has, while still warm, a peculiar odor, which dis- 

 appears more or less completely on cooling, and returns when the 

 urine is gently heated. The ordinary quantity of urine discharged 

 daily by a healthy adult is about Jxxxv, and its mean specific 



