followed by no irregularities."

These checks have their origin in a need for, and scarcity of
food,--food comprising all those conditions necessary to healthy life.
The need of food is vital and permanent. The desire for food, immediate
and prospective, is the first motive of all animal activity, but the
amount of food available in the world is limited, and the possible
increase of food is estimated by Malthus at an arithmetical ratio.

Whether or not this is an accurate estimate of the ratio of food
increase is immaterial. Malthus's famous progressions, the geometrical
ratio of increase in the case of animals, and the arithmetical ratio of
increase in the case of food, contain the vital and irrefutable truth of
the immense disproportion between the power of reproduction in man and
the power of production in food.

Under the normal conditions of life, the population tends constantly to
press upon, and is restrained by the limits of food. The true
significance of the word _tends_ must not be overlooked, or a similar
fallacy to that of Nitti's will occur, when he overlooked the
significance of the term "power to multiply." It is perfectly true to
say, that population _tends_ to press upon the limits of subsistence,
and unrestrained by moral means or man's reason actually does so.

Some social writers appear to think that, if they can show that
production has far outstripped population, that, in other words,
population for the last fifty years at least has _not_ pressed upon the
limits of food, Malthus by that fact is refuted.

Nitti says (Population and the Social System, p. 91), "But now that