MINERAL METABOLISM 373 



Chloride 



Animals get tlieir chloride largely in the form of the sodium salt. 

 The two ions are closely associated in many of their roles. Chloride 

 and sodium are particularly important in the maintenance of proper 

 osmotic concentrations in fluids and cells. Furthermore, chloride is 

 involved somewhat indirectly in the transport of carbon dioxide by 

 the blood. The chloride ion is important as a major electrolyte in 

 controlling the solubility of proteins, especially the globulins. 



Chloride is found throughout the tissues of animals and is adsorbed 

 to a considerable extent to proteins, altering their zeta potentials. 

 About two-thirds of the anions of blood are Cl~ with a normal con- 

 centration in the serum near 0.36 per cent. The interstitial fluid is 

 about the same. Red cells, on the other hand, range from 0.19 to 0.23 

 per cent C1-, and urine contains about 0.60 per cent Cl~ more or less. 

 Blood levels depend to a small extent on the quantity ingested, the 

 volume of liquid drimk, and the amount lost in urine and perspira- 

 tion. The chloride in the erythrocytes varies during the ionic ex- 

 changes accompanying carbon dioxide transport by the cells. In urine 

 the concentration of chloride varies much more and depends closely 

 on the amoimt of Cf- eaten and the volume of urine, thus ranging 

 widely from time to time during the day. 



Under normal conditions human beings and animals need dietary 

 C1-, but the quantity essential is difficult to ascertain. On a diet not 

 containing chloride, none is excreted in the urine after a few days. 

 Thus the body effectively conserves its supply. Since plants tend to be 

 somewhat low in both Na+ and CI", herbivores need supplementary 

 salt. Animal tissues are high in salt by contrast, and the carnivores get 

 plenty in their usual foods. Omnivores like man and swine ordinarily 

 get enough Cl~ unless restricted to purely vegetable diets. 



Deficiencies occur in cattle, sheep, and even deer unless salt is made 

 available. The porcupine is legendary in his patient search for salt. 

 Even horses may need salt in hot weather wlu"lc working hard and 

 sweating profusely and repeatedly. Human beings develop deficiencies 

 under similar conditions. For example, miners working at elevated 

 underground temperatures may lose salt at the rate of 2 g. per hour, 

 which must be replaced if the loss is at all prolonged. Deficiencies may 

 also occur after extended vomiting or diarrhea and are characteristic 

 of Addison's disease, a kidney malfunction leading to rapid loss of both 

 Na+ and C1-. The symptoms of salt deficiency include abdominal 

 cramps, weakness, rapid loss of weight, and cardiovascular disturb- 



