One great fundamental principle of preventive medicine is to keep infection from spreading beyond the sick. This principle has long been recognized in the case of very contagious diseases, such as smallpox, measles, etc., and here the methods employed are as yet purely empirical. In recent times the same principle has been applied to other diseases, like tuberculosis, typhoid fever, cholera, dysentery, etc., and in these the practical methods employed are the direct outgrowth of scientific investigations. Thus no conscientious physician at the present time would release a convalescent typhoid patient from restraint so long as the urine contains typhoid bacilli.
Pneumonia appears to be one of the last of the great infectious diseases to be put under the full domination of the principles of prevention of further spread.
The frequency and fearful destructiveness of pneumonia make it absolutely imperative that much greater attention than heretofore must be given to