522 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



so far as to produce vital disturbances, but the physiological minimum is 

 probably very low. A dog weighing 35 kilograms may live on 0.6 gram of 

 salt daily. 1 Sodium chloride, f'c<h produces of itself alone an increase of 

 water in the urine. If sodium chloride or other salts act as diuretics and 

 remove water from the tissues, an increase in proteid metabolism results. 

 Simple withdrawal of part of the water from the tissues raises the proteid 

 metabolism but does not affect the amount of fat burned. 2 



Sodium sulphate, Xa_,S( ) 4 , called " Glauber's salt," is found together with 

 potassium sulphate in the urine in the condition of preformed sulphuric acid 

 (see p. 507). If fed, it reappears in the urine. It acts on the epithelial cells 

 of the intestines, preventing the absorption of water, consequently causing diar- 

 rhoea. Other laxatives act in the same way. 



Sodium Phosphates. — The primary (NaH 2 P0 4 ) and the secondary 

 (Xa.,HP0 4 ) salts are found to a small extent iu the blood-plasma and other 

 Huids, and in the urine. As with the potassium phosphates, carbonic oxide 

 acts when in certain excess to convert the secondary phosphate into NaH,P0 4 

 and XaIIC0 3 . These two, however, may react on one another to drive off car- 

 bonic acid (seep. 517). Carnivorous urine owes its acid reaction principally 

 to primary sodium phosphate. If a mixture of NaH 2 P0 4 and Na 2 HP0 4 be 

 permitted to diffuse through membranes, the NaH 2 P0 4 passes through in 

 greater quantity, and this process may take place in the kidney. 3 Secondary 

 sodium phosphate dissolves uric acid on warming, forming sodium acid urate 

 and primary phosphate, which solution reacts acid (Voit). Urine standing in 

 the cold precipitates uric acid with the formation of secondary phosphates, 

 while the reverse reaction with return of original acidity takes place on warm- 

 ing the urine. 



Sodium Carbonates. — Of these there are two, the primary, NaHC0 3 , and 

 the neutral, XaX '( )... The organism owes its alkaline reaction, and also its 

 power of combining with carbonic acid, almost entirely to sodium carbonate. 

 Saliva, pancreatic and intestinal juice arc strongly alkaline with sodium carbon- 

 ate, as are also blood, lymph, and other Huids. If the organism be acidified, by 

 feeding acid to a rabbit, for example, death occurs even before complete loss 

 of the blood'- alkalinity, while venous injections of sodium carbonate at the 

 proper time restore the animal. Carbonic oxide cannot be removed from the 

 ti—ues in the acidified blood. Sodium carbonate treated with carbonic acid 

 becomes acid sodium carbonate, and this change; is effected in the internal res- 

 piration, where the cells give C0 2 to the blood. Treated with acids, both car- 

 bonates liberate carbonic oxide — a reaction which takes place in the blood 

 (see p. 517). Bunge suggests that the acid chyme of the stomach, into whose 

 finest particle- the alkaline intestinal juice' diffuses, i- especially penetrable by 

 the hitter's enzymes, because liberated carbonic oxide has separated the particles 

 of chyme from each other. The same principle would hold true of a morsel 

 well mixed with saliva, which, as is well known, is more easily penetrable by 



1 Voit: ]!■ rniiiiin'x Iltimllnirh, 18S1, vi. 1, S. 307. 



*Straub: ZeiUchriflfiir Biologk, 1899, Bd. 38, S. 537. 



3 Soubiranski : Archiv fiir expqr. Pathologu und Pharmakologie, 1895, Bd. 35, S. 178. 



