SECRETION. 441 



Physical Properties and Chemical Composition of the Urine. 



The analytical study of the urine is of great value to the physi- 

 cian and surgeon because of the knowledge which it gives concern- 

 ing the processes of metabolism occurring within the body. The 

 nature and amount of the various end-products of metabolism are 

 carefully investigated as they occur in the urine, whether they be 

 normal or pathological. From these investigations corresponding 

 conclusions are drawn. 



Neutral substances are, normally, either absent or present in 

 but minutest quantities. All of the important and more abundant 

 constituents of normal urine are either basic or acid in reaction. 

 These bases and acids must, therefore, enter into various combina- 

 tions, making the urine a solution of salts. The quantity of separate 

 ingredients found analytically might lead the observer to consider 

 the metabolic processes as pathological, yet in solution perfectly nor- 

 mal compounds are formed by these same components. The error 

 is due to the inability to study the properties of the urine as a com- 

 plex unit: the effects certain components have on others, their 

 avidity for one another, and the consequent equilibrium established. 



The Urine, The normal human urine, recently passed, is a clear 

 liquid of a straw color. It has an average specific gravity of 1.020, 

 is of aromatic odor, and a salty bitter flavor. In reaction it is acid; 

 only in pathological conditions does it become neutral or alkaline. 



Receding from the temperature of about 100 F., which is pro- 

 per to it in the act of passing, it loses its aromatic odor and acquires 

 a peculiar odor, described as urinous. In healthy persons it has 

 been seen to be phosphorescent during micturition, probably from 

 the liberation of phosphorus by its salts. In cooling, urine becomes 

 turbid, with a small cloud suspended in the thickness of the liquid, 

 formed from the epithelium of the uriniferous tubules. It leaves, 

 besides, especially if very much colored, sediments of different 

 appearance, according to the varying composition. 



The quantity of urine secreted by the kidneys of a healthy adult 

 man in twenty-four hours ranges from 1200 to 1700 cubic centi- 

 meters, or about 50 ounces ; in females the quantity is less. During 

 sleep the amount secreted is less than at other times, so that the 

 minimum secretion is placed between 2 and 4 A. M. and the maximum 

 from 2 to 4 p. M. 



While the average daily secretion is placed at 50 ounces, yet it 

 must be borne in mind that this quantity is not fixed, but may be 

 very variable, dependent upon numerous conditions. 



