[135] The higher standard need not be, among the mass of the population, of a very exalted character, although it marks a real progress. Newsholme and Stevenson (_op. cit._) term it a higher "standard of comfort." The decline of the birth-rate, they say, "is associated with a general raising of the standard of comfort, and is an expression of the determination of the people to secure this greater comfort." [136] Ploss, _Das Weib_, Vol. I, chap. XX. [137] It must not, however, be assumed that the rural immigrants are in the mass better suited to urban life than the urban natives. It is probable that, notwithstanding their energy and robustness, the immigrants are less suited to urban conditions than the natives. Consequently a process of selection takes place among the immigrants, and the survivors become, as it were, immunized to the poisons of urban life. But this immunization is by no means necessarily associated with any high degree of nervous vigour or general physical development. [138] Havelock Ellis, _A Study of British Genius_, pp. 22, 43. [139] "National Health: a Soldier's Study," _Contemporary Review_, January, 1903. The Reports of the Inspector-General of Recruiting are said to show that the recruits are every year smaller, lighter, and narrower-chested. [140] This has been well illustrated during the past forty years in the flourishing county of Glamorgan in Wales, as is shown by Dr. R.S. Stewart ("The Relationship of Wages, Lunacy, and Crime in South Wales," _Journal of Mental Science_, January, 1904). The staple industry here is coal, 17 per cent of the population being directly employed in coal-mining, and wages are determined by the sliding scale as it is called, according to which the selling price of coal regulates the wages. This leads to many fluctuations and sudden accesses of prosperity. It is found that whenever wages rise there is a concomitant increase of insanity and at the same time a diminished output of coal due to slacking of work when earnings are greater; there is also an increase of drunkenness and of crime. Stewart concludes that it is doubtful whether increased material prosperity is conducive to improvement in physical and mental status. It must, however, be pointed out that it is a sudden and unstable prosperity, not necessarily a gradual and stable prosperity, which is hereby shown to be pernicious.