Such indications of hygienic progress in our towns are not, however, sufficient to justify any expectation that the life of industrial towns will be made as healthy as that of the country. It is not possible to ignore the fatal significance of the continuous flow of an increasing proportion of the younger, healthier, and more vigorous part of the country population into town life. Dr. Ogle, who has collected much evidence upon this subject, sums up as follows:--"The combined effect of this constantly higher mortality of the towns, and of the constant immigration into it of the pick of the rural population, must clearly be a gradual deterioration of the whole, inasmuch as the more energetic and vigorous members of the community are consumed more rapidly than the rest of the population. The system is one which leads to the survival of the unfittest." § 5. Not only is life on an average of shorter duration in the towns, but it is of inferior physical quality while it lasts. The lowering of the townsman's physique not merely renders him less able to resist definite assaults of disease but injures his general capacity of work and enjoyment. This progressive deterioration of physique accounts for the unceasing flow of fresh country blood into the towns. In spite of the advantage of possession and knowledge of the town, the townsman cannot hold his own in the competition for town work; the new-comer jostles the old-comer from the best posts, and drives him to depend upon inferior and more precarious occupations for a living. Economic conditions, acquired social tastes, and impaired powers of physical labour prevent the feeble town blood from flowing back into the country to recruit its vigour. Hence the _impasse_ which forces problems of town poverty and incapacity ever more prominently upon the social reformer. In dealing with the diseases of occupations, Dr. Arlidge says, "It is a most difficult problem to solve, especially in the case of an industrial town population, how far the diseases met with in it are town-made and how far trade-made; the former almost always predominate."[280] It is not indeed possible to clearly distinguish the two classes of effects. Since machinery makes the industrial town, it makes it as a place to work in and a place to live in, and though certain trade conditions will operate more directly upon the inhabitants as workers, their effects will merge with and react upon the life-conditions of the town. The special characteristics of town work which cause ill-health and disease are-- (_a_) The predominance of indoor occupations, involving unwholesome air. (_b_) The sedentary character of most work in factories or workrooms, or otherwise the lack of free play of physical activities. (_c_) The wear and tear of nerve fibre (_e.g._, in boiler-making, weaving sheds, etc.).