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.