Excretions 



VICTOE C. MYERS 



NEW YORK 



There are four mediums for the excretion of waste products from 

 the body, viz., urine, feces, perspiration and expired air. Under normal 

 conditions and on a readily digestible diet, nearly 100 per cent of the 

 carbohydrate, about 95 per cent of the fat and more than 90 per cent 

 of the protein if no correction is made for the "metabolic nitrogen" of 

 the feces are completely digested and absorbed. The carbohydrate and 

 fat absorbed are almost entirely converted to carbon dioxid and water, 

 and this is also true of the carbon moiety (about 80 per cent) of the 

 protein. The carbon dioxid thus formed is excreted by way of the 

 lungs, as is a large amount of the water in the form of water vapor. 

 Considerable water may be lost from the body by way of the perspiration 

 but the amount of solids excreted in this way is never large, although with 

 severe exercise and sweating from 0.3 to 0.5 gram of nitrogen and 0.5 to 

 1.5 grams of sodium chlorid may be eliminated. The chief paths for 

 the excretion of solids are the kidney and intestine, the daily elimination 

 by these two channels in the adult amounting to about 50 grams in the 

 urine arid 30, grams in the feces. The nitrogenous waste products find 

 their principal exit through the kidneys, but in the case of the mineral 

 elements the kidneys and intestines both take part, the salts of sodium 

 and potassium being largely eliminated in the urine, while the salts of 

 calcium, magnesium and iron are excreted in the feces. Although the 

 excretion of the latter compounds in the feces may be due in part to lack 

 of absorption, still there is likewise a definite selective action regarding 

 their excretion. An excellent illustration of how changes in compounds 

 may affect their mode of excretion is the elimination of the two phenol- 

 phthalein derivatives, phenolsulphonephthaleiii and tetrachlorphthalein. 

 The former is eliminated entirely by the kidneys, while the latter after 

 being secreted in the bile by the liver is excreted by way of the intestines. 



Urine 



Since the end products of the metabolism of nitrogenous and mineral 

 substances find their principal exit through the kidneys, a study of the 



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