EXCRETION". 



471 



bouic or vegetable acids ; for these latter are changed into alkaline carbonates 

 previous to elimination by the kidneys. 



Average daily quantity of the chief urinary constituents (modified from Parkes). 



72. 



Variations in the Quantity of the Constituents. From the propor- 

 tions given in the above table, most of the constituents are, even in 

 health, liable to variations. The variations of the water in different 

 seasons, and according to the quantity of drink and exercise, have al- 

 ready been mentioned. The water of the urine is also liable to be influ- 

 enced by the condition of the nervous system, being sometimes greatly 

 increased, e.g., in hysteria and in some other nervous affections; and at 

 other times diminished. In some diseases it is enormously increased; 

 and its increase may be either attended with an augmented quantity of 

 solid matter, as in ordinary diabetes, or may be nearly the sole change, 

 as in the affection termed diabetes insipidus. In other diseases, e.g., 

 the various forms of albuminuria, the quantity may be considerably 

 diminished. A febrile condition almost always diminishes the quantity 

 of water; and a like diminution is caused by any affection which draws 

 off a large quantity of fluid from the body through any other channel 

 than that of the kidneys, e.g., the bowels or the skin. 



Method of Estimating the Solids. A. useful rule for approximately estimating 

 the total solids in any given specimen of healthy urine is to multiply the last 

 two figures representing the specific gravity by 2. 33. Thus, in urine of sp. 

 gr. 1025, 2. 33 X 25 58. 25 grains of solids, are contained in 1000 grains of the 

 urine. In using this method it must be remembered that the limits of errors 

 are much wider in diseased than in healthy urine. 



Variations in the Specific Gravity.- -The average specific gravity of 

 the human urine is about 1020. The relative quantity of water and of 

 solid constituents of which it is composed is materially influenced by 

 the condition and occupation of the body during the time at which it is 



