By a series of experiments on plants Doubleday discovered that "whatever
might be the principle of manure, _an overdose_ of it invariably induced
sterility in the plant." Although his formula is deficient in that food is
selected as the one factor in environment which influences fertility, and
although it may be an overstatement to claim that fertility varies in exact
proportion to abundance or to scarcity, nevertheless his formula contains
an important truth which literally knocks the bottom out of the whole
Malthusian case.

It is a sad reflection that, while the falsehoods of Malthus have been
blindly accepted for the greater part of a century, the work of Doubleday
was almost lost in oblivion. His shade has now been recalled to the full
centre of the stage, and for this the credit is due to Mr. C.E. Pell. His
recent book [52] is a stimulating essay on the declining birth-rate, and
contains much evidence that supports the main contention of Doubleday.
Although it is impossible to agree with all the deductions made by Mr.
Pell, he has nevertheless done a public service by restating the problem of
the birth-rate in a new way, by effectively bursting the Malthusian bubble,
and by tabulating fresh evidence against the birth-controllers.


Section 2. MR. PELL'S GENERALISATIONS CRITICISED

Mr. Pell defines the law of births and deaths in two generalisations. The
first is: "We have seen that it is a necessary condition of the success
of the evolutionary scheme that the variation of the inherited potential
degree of fertility between species and species must bear an inverse
proportion to their capacity for survival." [53] At first glance this
statement appears hard to be understood; but it is obviously true--because