In principle, the work-stuff stored in the muscles of the new-born child
is comparable to that stored in the gun-barrel. The infant is launched
into altogether new surroundings; and these operate through the
mechanism of the nervous machinery, with the result that the potential
energy of some of the work-stuff in the muscles which bring about
inspiration is suddenly converted into actual energy; and this,
operating through the mechanism of the respiratory apparatus, gives rise
to an act of inspiration. As the bullet is propelled by the "going off"
of the powder, as it might be said that the ribs are raised and the
midriff depressed by the "going off" of certain portions of muscular
work-stuff. This work-stuff is part of a stock or capital of that
commodity stored up in the child's organism before birth, at the expense
of the mother; and the mother has made good her expenditure by drawing
upon the capital of food-stuffs which furnished her daily maintenance.