Disease plays such a large part in the life of man and is so closely related to all of his activities that the changes in this period must have exerted an influence on disease.  We have already seen that within the period we have obtained knowledge of the causes of disease and the conditions under which these causes became operative.  The mystery which formerly enveloped disease is gone; disease is recognized as due to conditions which for the most part are within the control of man, and like gravity and chemical attraction it follows the operation of definite laws.  There has been developed within the period what is known as preventive medicine, which aims rather at prevention than cure, and the resources of prevention are capable of much greater extension.

Have there been new conditions developed within the period, or an increase of existing conditions which can be regarded as disease factors and which counterbalance the results which have come from the knowledge of prevention and cure?  There has been an increase of certain factors of immense importance in the extension of disease.  These are: 

1.  The increase in industrialism, involving as this does an increase in factory life.  In many ways this is a factor in disease. (a) By favoring the extension of infection, particularly in such diseases as tuberculosis. (b) The life indoors, and frequently with the combination of insufficient air and space, produces a condition of malnutrition and deficient general resistance. (c) The family life is interfered with by the mothers, whose primary duty is the care of home and children, working in factories, and the too frequent conversion of the house into a factory. (d) The influence of factory life is towards a loss of moral stamina rendering more easy of operation the conditions of alcoholism and general immorality.  How great has been this increase in industrialism, fostered as it has been by conditions both natural and artificially created by unwise legislation, is shown in the figures from the last census.  The number of factory operatives increased forty per cent between 1899 and 1909 and the total population of the country in the period between 1900 and 1910 increased twenty per cent.  It is probable that the future will see an extension rather than a diminution of mass labor.

2.  The increase in urban life is as conspicuous as the increase in industrialism.  In 1880, twenty-nine and five-tenths per cent of the population was urban and seventy and five-tenths per cent was rural; in 1910, forty-six and three-tenths per cent was urban and fifty-three and seven-tenths was rural, the increase being most marked in cities of over five hundred thousand inhabitants.  Of the total increase in population between 1900 and 1910, seven-tenths per cent was in the cities and three-tenths per cent in the country.  City life in itself is not necessarily unhealthy and there are many advantages associated with it.