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of view by saying that the amount of force required for this 
purpose would lift the man's body a little more than two (2*18) 
miles in the air during the twenty-four hours. 
From similar, though perhaps somewhat more doubtful 
calculations, Dr. Haughton estimates that the amount of 
bodily waste which is caused by one hour's hard mental labour 
involves an expenditure of force which is equal to lifting 
111 tons one foot in the air. 
Let us further suppose that, in addition to the mere act of 
living, an average man of 150 lb. weight undergoes bodily labour 
equivalent to lifting 200 tons one foot daily, and that the total 
amount of his day's mental work is equivalent to two hours' 
hard study, and the “ little bill"- of his daily expenditure of 
force will stand as follows : — 
Vital work 300 ‘00 grains of urea = 769 foot-tons 
Bodily work 7 7 ’38 „ „ = 200 „ 
Mental work 86*00 ,, „ = 222 „ 
Total urea 463*38 = 1191 tons raised one foot ; 
or one ton raised 1191 feet ; or the weight of the man’s body (150 lb.) 
raised a little more than 3 miles. 
To balance this side of his debtor and creditor account, our 
average man would have to consume an amount of food suffi- 
cient to furnish him with the nitrogen contained in 463 grains 
of urea. Hence he will find it desirable to take a considerable 
portion of animal food in his diet, because that kind of food 
contains, in proportion to its bulk, a much larger quantity of 
nitrogen than vegetable substances do ; for if he does not do 
this, he will have to augment the amount of vegetable material 
which he ingests to such an extent as seriously to embarrass 
his digestive functions. It is for this reason that the labour- 
ing man, who cannot procure meat for his daily meal, has 
recourse to cheese, which, although difficult of digestion, con- 
tains a considerable quantity of nitrogen. 
But, the reader may not improbably ask, if all this enormous 
quantity of force is expended by a living man during the short 
space of twenty-four hours, whence does it all come ? And 
this is a question which it is by no means easy to answer clearly 
within the limited space which is left to us. In general terms, 
however, it may be said that the force which the animal 
economy expends in the discharge of its various functions, is 
intimately incorporated with the food which it ingests for the 
support of its material framework. Animals live at the expense 
either of other animals or of vegetables — in both cases of pre- 
viously organized structures. Every process of organization 
involves the absorption and fixation of force in the created 
