CHAPTER LXI 



THE AMOUNT AND COMPOSITION OF THE URINE IN HEALTH 



AND DISEASE 



(Partly contributed by R. G. PEARCE) 



In the chapters on digestion and metabolism, we have followed the 

 course which food takes with especial reference to the nutrition of the 

 body. The excretion of these elements of nutrition is taken up under a 

 number of the subdivisions of physiology, viz., respiration, digestion, 

 kidney function and the skin. In the chapters on digestion attention was 

 called to the fact that the feces, besides containing the indigestible resi- 

 due of the aliment, contain several excretory products which at one 

 time or another have actually been within the body proper. These in- 

 clude normally the pigments of the body and many of the heavier mineral 

 salts, such as iron, magnesium, lime and phosphates; and under abnormal 

 conditions, as when the metals are given as medicine, bismuth and mer- 

 cury. The respiratory system excretes most of the oxygen and carbon. 

 In this chapter we shall take up the manner in which the body rids itself 

 of the nitrogenous, and some of the mineral waste materials. Even at 

 the risk of repetition, it will be advantageous to recapitulate certain facts 

 concerning the essential chemical structure of the urinary constituents, 

 so that we may be in a position to appreciate the kidney function in 

 health and disease. 



We now know that the kidney does not form any of the specific con- 

 stituents of its secretion (except hippuric acid). These substances are 

 formed in the various tissues of the body, and are brought to the kidneys 

 by the blood, where they are eliminated. But while the constituents in the 

 urine are unchanged in chemical composition from that in which they 

 are found in the blood, they do occur in greatly changed proportions. 

 It is this variation in the concentration of the urinary constituents in 

 the blood and the urine which presents the most important and at the 

 same time the most difficult question in the physiology of the kidney. 

 In the following table the percentage composition of the blood plasma is 

 compared with that of an average sample of human urine. The third 



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