A HARD-WORKING DIET. 21 
out as different compounds, are based upon careful 
observations and calculations. 
By such methods as these mentioned above we know 
the sum total of the C, H, O and N that is given off 
under different amounts of exercise or exertion. 
If the amounts given off in 24 hours are greater The materials 
than those taken in; if for example the amount of pee 
carbonic acid given off is greater than can _ be 
accounted for by the oxidation of carbon taken in, 
then it is evident there has been a demand made on 
what has been previously stored up in the body. It 
is well known that people store up fat who habitually 
take more carbon and hydrogen than the body 
actually demands for the work they do, and often 
store it up to an extent inconvenient to themselves. 
And the reverse of this is also known, that additional 
exertion without increase of carbon and hydrogen 
leads to a reduction of fat, and that a total amount of 
food inadequate to meet the daily demands, so uses 
up the stores, that emaciation follows. 
It has been found that the harder the work a man Carbon used 
up in propor- 
does the more carbonic acid he gives off in his breath, tion to work. 
which means that more Carbon has been oxidized. The 
Oxygen comes freely in the air, the Carbon has to be 
takeninas food. Whena man is doing a spell of hard 
work he should therefore have a care he is taking in 
more Carbon than when he is doing light work. Those 
who are continually doing hard work need more 
than those doing light work. These are facts that 
do not rest simply on the experiments and calcula- 
tions of men of science, but have been found true 
by navvies. Two well-known instances are those of 
making a railway in Sicily and the laying of the 
