2 
IMPERIAL COLLEGE OF 
creta, by exhalation or transpiration, after having served 
for the production of the energy and heat necessary for 
the vital functions of the organism. In general, only 
children and convalescent persons retain certain parts of 
the resorbed nutrients, depositing them in the growing 
organs. 
The products of the oxidation and decomposition of 
the digested substances are continually ejected, any ac¬ 
cumulation of these in the tissues of the body causing 
disease and death. The majority of the carbon is exhaled 
in the form of carbon dioxide through the lungs, an inferior 
proportion only passes through the skin, while almost all 
the nitrogen reappears in the urine chiefly as urea, but to a 
small extent as uric acid and other compounds ; of the 
mineral substances of the food the greater part, especially 
those which are soluble in water, pass into the urine along 
with a large quantity of water, the rest into the feces. As 
a whole the excreta contain, in the case of adults, all the 
nitrogen and mineral matters of the food, and are distin¬ 
guished from the latter particularly by the low proportion 
of organic substances ; at earlier stages of life some of the 
nitrogenous and mineral substances of the latter, particularly 
phosphoric acid and lime, are laid down in the body. 
Thus the excreta, if properly collected, contain nearly 
all the fertilizing ingredients of the food ; and, owing to 
the deep disintegration the albuminoids have undergone 
during their passage through the body, are in a state highly 
fitted for feeding plants. If in most countries of Europe 
and America they are not largely resorted to as a manure, 
this is simply because of the great dilution of the vegetable 
nutrients contained in them, which so greatly influences the 
cost of transportation that the same amount of nutrients 
of equal or higher efficacy and in a very handy shape can 
be generally obtained in the form of concentrated commer¬ 
cial fertilizers (ammoniacal salts, nitrate of soda, phosphates. 
