ALIMENTATION. 77 



matters and of oil from the integument; and there is dis- 

 charge of undecomposed matter in the form of mucus from 

 intestinal and other passages, as well as certain substances 

 derived from the bile; but the total amount of loss from 

 such sources is comparatively small. Also, it is to be noticed, 

 that ammonia escapes from the body in minute quantities, 

 and that there is usually in the urine a distinct though small 

 quantity of uric acid, a product of less complete oxidation 

 of nitrogenous substance than urea. But urea, the principal 

 organic constituent of the urine, a material of the same 

 composition as cyanate of ammonia, and therefore one stage 

 removed from that perfect oxidation which results in carbonic 

 acid and ammonia, is the substance in the form of which by 

 far the greater part of the nitrogenous debris escapes from 

 the body. 



Keeping out of consideration the debris of food which 

 has never entered the system, but is discharged in the feeces, 

 the amount of nitrogen given off daily may be estimated at 

 250 grains,'' 4 and the amount of carbon which escapes in the 

 form of carbonic acid may be reckoned at 4000 grains; these 

 substances must therefore be daily introduced into the system 

 in those quantities in the shape of food, if the weight of the 

 body and its constitution are to be maintained. Supposing 

 the 250 grains of nitrogen to enter the system in the form 

 of albumen, then in consequence of urea containing a much 

 larger percentage of nitrogen and smaller percentage of 

 carbon in its composition than albumen, there will be liberated 

 in the conversion of the albumen into urea 755 grains of 

 carbon, or seven-eighths of the total amount which the albu- 

 men contains, to escape in the form of carbonic acid, while 

 the rest of the 4000 grains daily lost must be furnished by 

 additional supplies of food, which need not contain any nitro- 

 gen. The amount of solid food necessary for the preserva- 

 tion of health is thus regulated by the loss of substance from 

 the body; but as a certain quantity of the food always escapes 

 digestion, and is discharged, after traversing the alimentary 

 canal, without having entered the system, the supply taken 

 has to be in excess of what is required to make up for 

 systemic loss. It has been calculated that there are daily 

 * One ounce avoirdupois contains 437J grains. 



