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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.

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. If we designate the lives lost in battle, the killed and the wounded who die, as 1, the loss of the German army from disease in 1870-71 was 1.5, that of the Russians in 1877-78 was 2.7, that of the French in Mexico was 2.8, that of the French in the Crimea 3.7, that of the English in Egypt 4.2. The total loss of the German army in 1870-71 from wounds and disease was 43,182 officers and men, and this seems a small number compared with the 129,128 deaths from smallpox in the same period in Prussia alone. In the Spanish American war there were 20,178 cases of typhoid fever with 1,580 deaths.

In the South African war there were in the British troops 31,118 cases of typhoid with 5,877 deaths, and 5,149 deaths from other diseases while the loss in battle was 7,582. The Athenian plague which prevailed during the Peloponnesian war, 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 zoölogy and botany; it has given birth to the sciences of bacteriology and protozoölogy 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.

New York, Henry Holt And Company.
London, Williams and Norgate, originally published 1913

Tags: Infectious Diseases