564 WASTE-PRODUCTS 



in the proteins of a meat-diet are oxidized wholly or in part to the 

 highly dissociated sulphuric and phosphoric acids which decrease the 

 alkali-reserve of the blood and tissues and are excreted as acid salts in 

 the urine, while the alkaline salts in vegetables are oxidized to carbon- 

 ates or bicarbonates and excreted as such. 



According to Fitz and Van Slyke the titratable acidity of the urine 

 (employing phenolphthalein as an indicator) runs remarkably parallel, 

 in conditions of Acidosis, with the decrease of the alkali-reserve. In 

 order to observe this parallelism, however, we must add to the titrat- 

 able acidity the amount of Ammonia in the urine which has been 

 furnished by the tissues as a means of neutralizing a portion of the 

 excess of acid. This can be estimated by the method of Sorensen, the 

 Formol Titration, which depends upon the fact that formaldehyde in 

 faintly alkaline solutions unites with ammonia to form hexamthylene- 

 tetramine, which has a neutral reaction : 



4NH 4 C1 + 6 HCHO + 4 NaOH = N4(CH 2 ) 6 + 10 H 2 O + 4 NaCl 



The urine is first rendered very faintly alkaline to phenolphthalein, 

 then neutral formaldehyde is added and the quantity of alkali which 

 must be added to render the urine alkaline again is determined by 

 titration. This is equivalent to the ammonia which has been converted 

 into hexamethylene-tetramine. 1 



The relationship observed by Fitz and Van Slyke is expressed by 

 them in the following formula, which is an adaptation of the formula 

 of Ambard for the excretion of urea and chlorides: 



Bicarbonates in the plasma = 80 



where D.is the titratable acidity plus the ammonia output, W the 

 weight of the individual and C the concentration of acids in the urine, 



or -, where V is the volume of urine. The figure 80 represents the 



maximum yield of carbon dioxide in volumes per cent, which may be 

 obtained by treating blood-serum with sulphuric acid. Reduction of 

 the alkali-reserve below this point results in the urinary excretion of 

 an excess of acid radicals which is expressed by the factor: 



This relationship is purely empirical and the agreement between the 

 calculated and observed values of' the alkali-reserve cannot be relied 



1 The NH groups of amino-acids will react with formaldehyde in the same way 

 as ammonia. The concentration of amino-acids in the urine is so small, however, that, 

 as a rule it may be neglected. 



