134 PHYSIOLOGICAL CHEMISTRY. 



but forms a distinguishing constituent of the crystallizable matters of 

 the urine. Of these matters, urea is by far the most abundant, and 

 fully five-sixths of the nitrogen taken in with the food reappears as an 

 ingredient of urea, while the remainder is included in the creatinine 

 and uric and hippuric acids of the urine, and in the excrementitious 

 substance of the feces. 



There is evidence, however, that albuminous matters also take 

 part in the formation of carbonic acid ; that is, although all their nitro- 

 gen is discharged under the form of urea and other similar combina- 

 tions in the urine and feces, all their carbon does not appear in these 

 excretions, and must pass out by some other channel. While, as we 

 have seen, 130 grammes of albuminous matter are taken daily with the 

 food, containing 70 grammes of carbon, only 35 grammes of urea are 

 discharged during the same time, containing 7 grammes of carbon ; and, 

 according to the most accurate analyses,* not more than 23 grammes 

 are discharged daily by both the urine and feces together. This leaves 

 unaccounted for about 47 grammes of carbon, or two-thirds of the 

 original quantity, which must pass out from the body under some other 

 form of combination. The same thing is true, to a considerable extent, 

 of the hydrogen of these substances, of which 10 grammes are intro- 

 duced daily with the albuminous matters of the food, while not more 

 than 5 or 6 grammes are discharged in organic combinations with the 

 urine and feces. The albuminous matters, therefore, not only give rise 

 to the elimination of urea, but also contribute to the production of 

 carbonic acid and water. 



The manner in which this takes place is probably by the separation 

 of some of the elements of albumen, in the form of urea, while the 

 remainder are left behind as a non-nitrogenous substance. If we adopt, 

 for the constitution of an albuminous body, exclusive of its sulphur, 

 Lieberkuhn's formula, C 72 H 112 N 18 22 , and take away from it all the nitro- 

 gen in the form of urea, a substance will remain analogous in composi- 

 tion to a fat, thus 



Albumen . 73 H n2 N M O^ 



9 Urea (OH 4 N 2 O) C 9 H^ N 18 O 9 



CGS H 7G O 13 



The remaining substance may then undergo complete oxidation 

 without the further production of a nitrogenous compound. This 

 double result of the decomposition of the albuminous substances, to- 

 gether with the fact that we take habitually three or four times as 

 much non-nitrogenous as nitrogenous matter in the food, will explain 

 the preponderance of carbonic acid as an excretion over urea. For 

 while the average daily quantity of urea is only 35 grammes, the 

 carbonic acid exhaled with the breath amounts to from 700 to 800 

 grammes ; the quantity of carbonic acid produced being, by weight, 

 fully twenty times as great as that of the urea. Urea is a nitrogenous 



* Eanke, Grundziige der Physiologie des Menschen. Leipzig, 1872, p. 298. 



