HOW POPULATION INCREASES 61 
that of Germany afford notable examples of changes 
in the direction of more intense industrial development. 
It has to be borne in mind, however, that the attempt 
to support industries by high protective tariffs, without 
an equally self-denying ordinance being applied in the 
case of labourers engaged in secondary industries, tends 
to react in such a way that the conditions will not 
necessarily develop that are required to ensure a large 
population for the country in question. 
Though the part played in a country’s development 
of population by its measure of industrial advance is of 
very great importance, there are certain things to be 
borne in mind. The world, as at present organised, 
is apt to mislead as to its population possibilities, 
unless due account be taken of those just referred to. 
As pointed out by Sir Henry Rew, in his estimate in 
1912 of the food-production of the United Kingdom, 
and by Prof. E. M. East of Harvard, in 1923, in 
Mankind at the Cross-roads, many countries do not 
themselves supply directly their own food-require- 
ments by agriculture. The United Kingdom was 
estimated to produce only about 41 per cent. of its 
needs thus directly. According to Sir Henry Rew, in 
acres per head, the position of things was as follows: — 
Date. Farm area. Under plough. Wheat. Cattle per head. 
Year 1871 . .. 118 O71 014 0°20 
Year 1gix . . 079 036 005 017 
The situation existing was really what has already 
been stated, viz., that populations with great secondary 
industrial and similar developments purchase from 
outside countries much of their required foods, etc., 
with the products of their secondary industries. Hence, 
in any endeavour to estimate possible populations, it 
is but little use comparing merely areas. Switzerland, 
for example, produces 32:4 bushels per acre, but her 
cereals and food-crops together cover only 4 per cent.