142 TlMEHRI. 
Besides the supply of suitable food for the production 
of muscular power, it must be remembered that provi- 
sion has to be made for muscular maintenance. During 
rest, or comparative rest, the elimination of nitrogen 
amounts to from 150 to 200 grains per diem. This quan- 
tity may be said to represent the tissue destruction going 
on normally in the body. During work this amount 
would be somewhat increased by the increased wear of 
the tissues. Allowing an additional 50 grains for this 
would bring up the nitrogen to be supplied in the form 
of food to, say 275 grains; and no form is so good for 
the administration of this nitrogen as meat. This amount 
of nitrogen would be yielded by about 14 oz. of lean 
beef, but it must be remembered that even were a car- 
bo-hydrate chosen to yield the force-value a certain 
amount of nitrogen would be ingested therein, and thus 
a smaller quantity of meat would suffice. 
By adaptation of the above principles means are 
afforded for comparing the relative economy of manual 
and machine labour. I have stated that it is calculated 
that with man about one-fifth only of the dynamic value 
of the food is utilisable for work. With a steam-engine 
constructed on the most approved principles, only one- 
tenth of the force-value of the fuel is obtained. Were 
then the cost of food anywhere near the cost of fuel, 
man would be the cheaper engine for work. But be- 
tween the cost of food and that of fuel, there is an enor- 
mous difference, and it is this difference which gives rise 
to the economy of machine labour. 
Much discussion has taken place lately on the position 
which alcohol holds in relation to food. Calculated from 
