INFLUENCE OF INDUSTRIAL DEVELOPMENT 345 
rapidly than the inferior ones, and do they attract the better or 
the poorer stocks from the surrounding country? 
Probably the treatment of these questions which has suc- 
ceeded in arousing the most discussion in Hansen’s work Die 
drei Bevélkerungsstufen. Hansen divides the population into 
three classes: (1) the landowners from nobles owning estates to 
the peasants with small holdings, (2) the middle class consisting 
of officials, professionals, artisans, merchants, and (3) the prole- 
tariat and day laborers and people in general with scanty means 
of subsistence. Needless to say these are not well-defined groups 
and that there is a continual transfer from one group to another. 
The first class, the country dwellers, according to Hansen, con- 
stitute a large proportion of the rural contribution to the city 
population. It is this class that has the highest birth rate. Their 
surplus as a result of economic pressure flows to the cities where 
it supplies the second class with most of its members. Here they 
are subjected to conditions of life which enhance the death rate 
and reduce the birth rate so that, notwithstanding the superior 
economic status which they acquire, they rapidly diminish in 
number. Urban immigrants, according to Hansen, are of better 
average quality than those who remain to carry on agricultural 
pursuits. It is this rural influx that keeps up the vitality of urban 
populations, and is mainly responsible for urban growth. Many 
cities, were they dependent upon natural increase alone, would 
suffer an actual loss of population. Dr. Boeckh has estimated 
that the fertility of the city born in Berlin is not high enough to 
perpetuate the stock. Paris for a long time has not been self- 
sustaining. Lagneau calculated that were it not for immigration 
its population would decrease 50 per cent in each generation. 
Where cities grow through their own birth rate their increase is 
dependent upon the fertility of the proletariat, since the middle 
class is generally not self-perpetuating. Between the recruits 
coming from other classes and its own fecundity the third stratum 
perpetuates itself even under the unfavorable conditions into 
which it is forced through economic pressure. But through 
overcrowding, poor food and other destructive agencies, it tends, 
