FOOD. 129 



neous oxygen, since, beside their larger proportion of carbon, they also 

 contain hydrogen which requires further oxidation, in order to form 

 water. The change thus undergone by fatty substances may be ex- 

 pressed as follows : 



Fat. Carbonic acid. "Water. 



C 5 iH 98 6 + 145 = C 51 102 + H 98 0, 9 . 



In the case of the albuminous matters the process is a different one. 

 These substances contain an element, namely, nitrogen, which does not 

 appear in the carbonic acid and watery vapor of the expired breath, 

 but forms a distinguishing constituent of the crystallizable matters of 

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

 already mentioned, 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 the nitrogenous 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, 1 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 as an ingredient of the albuminous matters of the food, 

 while not more than 5 or 6 grammes are discharged in organic combi- 

 nations 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 combined as urea, after which the 

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

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

 the formula C 72 H 112 N 18 O 23 , and take away from it all the nitrogen in the 

 form of urea, a substance will remain analogous in composition to a 

 fat, th us- 



Albumen ..... C- 2 H 112 N 18 23 

 9 Urea (CH 4 N 2 0) . . . . C H 36 N 18 9 



1 Kanke, Grundziige der Physiologic des Menschen. Leipzig, 1872, p. 298. 



