The massing of the people in large cities, the factory life, the much greater social life, which are all prominent features of modern civilization, would be difficult or impossible without control of the infectious diseases.
The rapidity of communication and the increased general movement of people, which have developed in equal ratio with the massing, would serve to extend widely every local outbreak of infection.

The principles underlying fermentation and putrefaction which have been applied with great economic advantage to the preservation of food were many of them developed in the course of the study of the infectious diseases.

Whether the development of the present civilization is for the ultimate advantage of man may perhaps be disputed, but medicine has made it possible.
The infectious diseases appearing in the form of great epidemics have been important factors in determining historical events, for they have led to the defeat of armies, the fall of cities and of nations.

War is properly regarded as one of the greatest evils that can afflict a nation, since it destroys men in the bloom of youth, at the age of greatest service, and brings sorrow and care and poverty to many.

But the most potent factor in the losses of war is not the deaths in battle but the deaths from disease.