A brief checklist supports the authors' point that disease is a crucial determinant in history. Think first of the many famous victims of fatal maladies: Henry VIII and Ivan the Terrible (syphilis); Cromwell, Alexander the Great, Titus, Vespasian, Hadrian (malaria); Louis XV, Pericles, Marcus Aurelius, Mary II of England (smallpox), to name but a few. Then consider the wider impact of disease. To take British history alone, the reason Vortigern called in Hengist and Horsa in the fifth century was that England was so weakened by pestilence that it could no longer contain the marauding Scots and Picts. The Black Death in the 14th century almost halved the country's population over 30 years, from 4.5 million in 1347 to 2.5 million in 1377. It undermined the feudal system in England, cut the peasantry's ties to the land, weakened the hold of the Church and may have opened the way for the Reformation.
Fredrick Cartwright and Michael Biddiss illuminate every aspect of the historical toll of this dreaded Horseman of the Apocalypse in their absorbing and lucid study, Disease and History. Dealing with different visitations in each chapter, they distinguish carefully between insect-borne diseases (malaria, yellow fever, filariasis, sleeping sickness) and sickness caused by bacteria and viruses (smallpox, tuberculosis, cholera, typhus, typhoid), and then between the "act of God" pandemics and the epidemics caused by human carelessness (typhus is a dirt-based menace carried by infected lice, whereas typhoid is caused by the bacteria of human excrement). They list with clinical efficiency the sub-classes of malaria (blackwater fever, tertiary and quartan ague), of influenza (Spanish flu, Asian flu, Melbourne flu . . . ), and they are particularly good at identifying the crucial plague pandemics, such as that of Cyprian in 250, of Justinian in 542 and of the Black Death of 1348-61.
Some of the book's conclusions cannot be doubted. Nobody could question the deadliness of the 1918-19 flu pandemic as it carried off 50 million people, compared to the ten million who had been killed in the first world war. And disease certainly helped Cortes and the conquistadores to conquer Mexico, where the population declined staggeringly in the 16th century from an estimated 25 million to two million because of the spread of smallpox. Nor can it be contested that the conquest of malaria and other tropical diseases enabled the great Victorian explorers to penetrate the "Dark Continent". The authors also provide an exemplary, admirably judicious discussion of syphilis: did it come to Europe from the West Indies after Columbus's voyages, or did it originate in Africa, to be introduced into Europe by African slaves?
However, the authors often seem determined to stretch the historical evidence farther than it will go. To claim that the "great plague" in Athens in 429 BC won the Peloponnesian war for Sparta ignores crucial factors such as the military debacle in Syracuse of 415-13. And while it may be the case that Christianity progressed as it helped to assuage the fear of death and prompted the cult of Christ the Healer, it is an overstatement to say that Christianity could not have triumphed in the Roman world had not malaria and other pestilence fatally weakened the empire. Again, while it is true that typhus attacked Napoleon's army on the outward march to Moscow in 1812, this was a minor factor in the French conflict of that year. But the authors very nearly make it the cause of Napoleon's downfall.
Cartwright and Biddiss acknowledge that the aetiology of organic disease is monocausal, but they sometimes fall into the trap of isolating the impact of pestilence as the historical motor. There are signs that, in this revised edition of a work first published in 1972, the authors have not kept up with all the most recent historical scholarship. It is no longer possible to state with categorical certainty, as they do, that Napoleon died of cancer; indeed, this theory now seems highly unlikely. The best opinion, too, is that the Athens epidemic that carried off Pericles in 429 BC was probably neither plague nor scarlet fever but smallpox. The revised bibliography is also deficient in recent titles: there is no mention of Desowitz on mosquitoes and malaria, Ransford on tropical diseases, or Ford on sleeping sickness. Yet these blemishes scarcely detract from the overall worth of a study whose outstanding virtues are economy, clarity and readability.
The writer's "Villa and Zapata: a biography of the Mexican revolution" is published in June (Jonathan Cape, £18.99)