CHAPTER V.
INFECTIOUS DISEASES .-- THE HISTORICAL IMPORTANCE OF EPIDEMICS OF DISEASE .-- THE LOSSES IN BATTLE CONTRASTED WITH THE LOSSES IN ARMIES PRODUCED BY--INFECTIOUS DISEASES .-- THE DEVELOPMENT OF KNOWLEDGE OF EPIDEMICS .-- THE VIEWS OF HIPPOCRATES AND ARISTOTLE .-- SPORADIC AND EPIDEMIC DISEASES .-- THE THEORY OF THE EPIDEMIC CONSTITUTION .-- THEORY THAT THE CONTAGIOUS MATERIAL IS LIVING .-- THE DISCOVERY OF BACTERIA BY LOEWENHOECK IN 1675 .-- THE RELATION OF CONTAGION TO THE THEORY OF SPONTANEOUS GENERATION .-- NEEDHAM AND SPALLANZANI .-- THE DISCOVERY OF THE COMPOUND MICROSCOPE IN 1605 .-- THE PROOF THAT A LIVING ORGANISM IS THE CAUSE OF A DISEASE .-- ANTHRAX .-- THE DISCOVERY OF THE ANTHRAX BACILLUS IN 1851 .-- THE CULTIVATION OF THE BACILLUS BY KOCH .-- THE MODE OF INFECTION .-- THE WORK OF PASTEUR ON ANTHRAX .-- THE IMPORTANCE OF THE DISEASE.
These are diseases which are caused by living things which enter the tissues of the body and, living at the expense of the body, produce injury.

Such diseases play an important part in the life of man; the majority of deaths are caused directly or indirectly by infection.

No other diseases have been so much studied, and in no other department of science has knowledge been capable of such direct application in promoting the health, the efficiency and the happiness of man.

This knowledge has added years to the average length of life, it has rendered possible such great engineering works as the Panama Canal, and has contributed to the food supply by making habitation possible over large and productive regions of the earth, formerly uninhabitable owing to the prevalence of disease.

It is not too much to say that our modern civilization is dependent upon this knowledge.