The general acceptance of the bacillus discovered by Koch as the exciting cause of tuberculosis in man and the food animals is based on the most careful experimental observations. Without the bacillus there can be no tuberculosis. Therefore, if we should destroy all these bacilli there would be an end to tuberculosis. This appears to some logical, simple and, to a degree, possible of attainment. It is a sequence of cause, effect and prevention which has produced a revolution in medical thought and action.
Whereas formerly an occasional instance of apparent communication of the disease from one individual to another excited some speculation as to its possible contagiousness, or was explained by heredity or coincidence, now all is changed—infection or communication from another is almost universally recognized as the essential factor.
Tuberculosis then being an infectious disease affecting a larger number of individuals than any other, it naturally falls into