431-405 B.C., not only caused the death of Pericles, but according to Thucydides a loss of 4,800 Athenian soldiers, and brought about the downfall of the Athenian hegemony in Greece.  In the Crimean war between 1853-56, 16,000 English, 80,000 French and 800,000 Russians died of typhus fever.  The plague contributed as much as did the arms of the Turks to the downfall of Constantinople and the Eastern Empire in 1453.  It was the plague which in 1348 overthrew Siena from her proud position as one of the first of the Italian cities and the rival of Florence, and broke the city forever, leaving it as a phantom of its former glory and prosperity.  The work on the great cathedral which had progressed for ten years was suspended, and when it was resumed it was upon a scale adjusted to the diminished wealth of the city, and the plan restricted to the present dimensions.  As a little relief to the darkness the same plague saw the birth of the novel in the tales of Boccaccio, which were related to a delighted audience of the women who had fled from the plague in Florence to a rural retreat.

The knowledge which has come from the study of infectious disease has served also to broaden our conception of disease and has created preventive medicine; it has linked more closely to medicine such sciences as zooelogy and botany; it has given birth to the sciences of bacteriology and protozooelogy and in a way has brought all sciences more closely together.  Above all it has made medicine scientific, and never has knowledge obtained been more quickening and stimulating to its pursuit.

Although the dimensions of this book forbid much reference to the historical development of a subject, some mention must still be made of the development of knowledge of the infectious diseases.  It was early recognized that there were diseases which differed in character from those generally prevalent; large numbers of people were affected in the same way; the disease beginning with a few cases gradually increased in intensity until an acme was reached which prevailed for a time and the disease gradually disappeared.  Such diseases were attributed to changes in the air, to the influence of planets or to the action of offended gods.  The priests and charlatans who sought to excuse their inability to treat epidemics successfully were quick to affirm supernatural causes.  Hippocrates (400 B.C.), with whom medicine may be said to begin, thought such diseases, even then called epidemics, were caused by the air; he says, “When many individuals are attacked by a disease at the same time, the cause must be sought in some agent which is common to all, something which everyone uses, and that is the air which must contain at this time something injurious.”  Aristotle recognized that disease was often conveyed by contact, and Varro (116-27 B.C.) advanced the idea that disease might be caused by minute organisms.  He says, “Certain minute organisms develop which the eye cannot see, and which being disseminated in the air enter into the body by means of the mouth and nostrils and give rise to serious ailments.”  In spite of this hypothesis, which has proved to be correct, the belief became general that epidemics were due to putrefaction of the air brought about by decaying animal bodies, (this explaining the frequent association of epidemics and wars,) by emanations from swamps, by periods of unusual heat, etc.