METABOLISM. 27 
bolism may properly be considered in connection with that of the 
carbohydrates themselves. 
But little is known of the metabolism of the organic acids, how- 
ever, beyond the fact that they are oxidized in the body, a portion 
of the resulting carbon dioxide appearing in the urine, in combina- 
tion with sodium and potassium, rendering that fluid alkaline. 
Wilsing * and v. Knieriem + have shown that organic acids such as 
result from the fermentation of carbohydrates are not found to any 
appreciable extent in the excreta, while the researches of Munk t 
and Mallevre,§ which will be considered more particularly in 
another connection, have shown that the sodium salts of butyric 
and acetic acids when injected into the blood are promptly oxi- 
dized, and Nencki & Sieber || have shown that lactic acid is 
readily oxidized, even by a diabetic patient. 
NON-NITROGENOUS MATTER OF THE URINE. 
It has been implied in the foregoing pages that. the digested 
carbohydrates of the food, whatever the intermediate stages through 
which they may pass, are ultimately oxidized to carbon dioxide and 
water. Of the ordinary hexose carbohydrates this is doubtless 
true, but with some of the large variety of substances ordinarily 
grouped together, by the conventional scheme of feeding-stuffs analy- 
sis, as “carbohydrates and related bodies,” or as “crude fiber’’ 
and “nitrogen-free extract,” the case appears to be otherwise. 
It has been shown that the urine, in addition to the nitrogenous 
products of proteid metabolism which will be considered in a 
subsequent section, contains also non-nitrogenous materials, pre- 
sumably metabolic in their nature. In the urine of man and of the 
carnivora these non-nitrogenous substances are chiefly or wholly 
such as might be derived from the metabolism of proteids (phenols 
and other compounds of the aromatic series), and their amount is 
comparatively small. In the urine of herbivora, particularly of 
ruminants, however, their quantity is relatively very considerable, 
and it seems impossible to regard any large portion of them as 
derived from the proteid metabolism. 
* Zeit. f. Biol., 21, 625. t Arch. ges. Physiol., 46, 322; 
+ Ibid., 21, 139. 8 Ibid., 49, 460. 
|| Jour. pr. Chem., N. F., 26, 32. 
