250 ANATOMY AND PHYSIOLOGY 



pale, as the urine contains less or more water. The weight is due 

 to the salts contained, both organic and inorganic (or mineral) and 

 this also is modified by the amount of water. Both water and salts 

 vary markedly with the dietary of the individual. 



Clinical notes. The color and odor may both be modified by drugs or by 

 articles of food. (For example, turpentine causes the odor of violets, while 

 that imparted by asparagus is well known.) Urine containing blood cells is 

 smoky in appearance; and every nurse knows what methylene blue will do. 



The most important substance to be excreted in the urine is 

 urea. This represents the absolutely useless material remaining 

 from protein foods. It is prepared for excretion in the liver. It 

 is a substance which if allowed to accumulate in the system 

 becomes a deadly poison, causing death by uremia. 



Uric acid is protein waste in another form and smaller quantity. 

 Phosphates of sodium, potassium and calcium are present normally, 

 also other mineral salts, sodium chloride (common salt) being the 

 most abundant. 



Water is necessary for the solution of all these solids. This 

 varies in quantity in many systemic conditions. Increased 

 activity of the lungs and skin, for example, removes water from 

 the blood and thus makes the urine scanty but more dense and 

 very acid. 



Two sets of causes affect the quantity of urine: i. those which increase 

 or diminish blood pressure in the kidney; 2. those which influence the secretory 

 activity of the cells which line the tubules. Increased blood pressure increases 

 the flow of water and salts (in the glomeruli) ; toxic substances (organic waste) 

 stimulate the excretory function of the cells in the tubules. 



The importance of the kidneys is shown by the fact that the 

 daily quantity of urine normally produced, equals the excretion 

 of the lungs, skin and intestinal tract together. 



The average amount of solids in the body (to be excreted) 

 does not vary greatly, but the quantity of water ingested varies 

 constantly and the specific gravity changes with the water supply. 



The quantity and the specific gravity bear a pretty constant ratio to 

 each other. As a rule, the abundant urine is light in weight (low specific 

 gravity). Conversely, the scanty urine is dense and heavy (high specific 

 gravity). A notable exception is the urine of diabetes mellitns, which is very 

 abundant and at the same time has high specific gravity, owing it to the 

 sugar content. 



