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Causes of Plague

The seventeenth-century Dutch physician Paul Barbette (1620-1666) on the causes of plague:

‘The cause of the Plague is either Internal or External: but unto which soever we impute it, it is necessary to conclude, that there is a power of dissolving the natural Consistence of the Blood, and depriving the whole Body of its strength. As to the Inward Cause, which is Meat and Drink, it is evident to all, that it cannot produce in any Body whatsoever so great and sudden a change; but it is most certain, that by a long and continued course of bad Diet, the Blood may by degrees be after such a manner dissolved, weakened, and corrupted, that some part of it assuming to it self a malignant quality, a man may be surprized by a sudden Disease, and sometimes be deprived of life it self…
As to the outward Causes, every one confesseth that there are such; but their Nature is known but to few: The Chymists, who are able by the force of Fire distinctly to separate the Parts of simple Drugs, endeavour to find the Original of the Contagion in a Volatile Salt, which suddenly dissolves the fixed Salt of the Blood; which hath indeed some appearance of truth, though ti will not be relished by all men.
If you enquire into the Cause hereof from others, their answer will be various, but most of them very idle and impertinent.
It hath by some been thought probable that a Plague might proceed from the Heavens; they affirming that the Stars do actuate the Sublunary Bodies, both by the influence of their light, and by several other qualities inherent in, and peculiar to them. But the Conjectures raised from hence, are very uncertain, and the foundation of them unsecure…
We know that the Air may be several wayes corrupted; from whence the Vapors which have been received from the Earth, are sent down again amongst us, which like Fire may inkindle our Blood, Corrupt waters, Carcasses either not at all buried, or else shallowly interred; the South-Wind, which may be supposed to promote the Putrefaction; Men already infected, and successively imparting the Contagion to the sound, and by that means spreading the Venom through the Bodies of Men, and the Air it self.
This Pestilential Infection may likewise for a long time lie couched and concealed in Straw or Stubble, amongst Garments, Hangings, and the Furniture of Beds; which we have sometimes observed strangely to impart their Malignity to those that have handled them, or approached unto them.
But all these things only inform us of the means by which this Pestilential Poyson is conveyed unto us; but no one hath as yet declared what it is, and wherein its Nature doth properly consist.’

Paul Barbette, Thesaurus Chirurgiae: The Chirurgical & Anatomical Works of Paul Barbette…
Together with a Treatise of the Plague…
(London, 1676), pp 345-7.

Barbette’s treatise on plague was attached to his texts on surgery and anatomy, a composite work which was so popular that it was not only translated into English but ran to four editions by 1687. At least one of the reasons for the popularity of Barbette’s work is clear in the above quotation: the clarity of his exposition of contemporary understanding of plague. Barbette’s analysis is a comprehensive one, incorporating as it does the principal seventeenth- (and eighteenth-) century explanations concerning the cause and methods of transmission of the disease.

Opinions varied widely. For François Chicoyneau, a French physician who literally had hands-on experience of the plague at Marseilles in 1720, the plague was a result of bad air, ‘mal aria’, a deduction which necessarily had therapeutic implications since if the theory was correct it made little sense to impose quarantine arrangements; Richard Mead, the celebrated London doctor who ruefully admitted that he was advocating measures to be taken for a disease ‘which I have never seen’, vehemently disagreed: his theory of contagion, a theory based on human to human contact, meant that quarantine would play an all important role in the defences of England against the Marseilles plague in 1720. If treatment for Chicoyneau had necessarily focussed on cure, for Mead it concentrated on prevention.

Plague was an umbrella term: it denoted an illness which seemed to have a host of forms and a nature as changeable as mercury. The extracts in this website on plague symptoms illustrates the difficulties faced by early modern physicians who sought to pin down the chief characteristics of the disease: for plague was simultaneously all pervasive and elusive: it might show itself in one guise in one neighbourhood at one specific time but change its form almost simultaneously. The only definite sign that was deemed by all to be characteristic of the disease were the infamous buboes: yet even these might be absent in some of the direst cases.

A flea, Philosophical transactions (London, 1716), p. 182.

It is now recognised that there was not one form of plague but at least three related clinical manifestations of bubonic plague: bubonic, septicaemic and pneumonic. Bubonic, with its characteristics buboes, was the most visible, if not the most fatal. We now know that the cause of bubonic plague is the bacillus Yersinia pestis, a micro-organism associated with the rat flea Xenopsylla cheopis which feeds off the black rat Rattus rattus. This dependence on rat fleas affects the progress of the disease through first the rodent population when the plague is in the enzootic form, through to the epizootic stage and finally to the epidemic involving humans. It thrives in warm conditions and therefore bubonic plagues were always at their height in the summer months, when an epidemic once it had broken out, quickly ran through the population, causing mortality rates of somewhere between 60-80% in the early modern period. If the disease made its way directly into the blood stream buboes might not have time to form for septicaemic plague would set in, inevitably causing death. Transmission in bubonic and septicaemic was therefore dependent on rat fleas, rather than human-to-human transmission and for this reason figures for these types of plague, though often fatal, were lower than the catastrophic figures that ensured once plague had taken its pneumonic form. This third type, pneumonic plague, was likewise related to bubonic plague: once the patient had caught bubonic they might contract pneumonia and in turn the epidemic figures would spiral as transmission no longer relied on rat-flea-human and now could be spread from human to human by coughing.

Because the fatality rate is so much higher for pneumonic plague it has sometimes been assumed that it was the culprit for the most infamous plague of all, the Black Death, when roughly one third of the population of Europe died. However, as Scott and Duncan have argued (2001), though pneumonic plague may have a different transmission pattern and symptoms it is not a distinct plague form: it was, in short, always associated with an initial outbreak of bubonic plague. To account for the levels of mortality, especially during winter months, they suggest the presence of another type of plague in early modern England: haemorrhagic plague, a viral plague not dependent on rat fleas for transmission.

Plague Today

To read more about plague today see the Worth Health Organization website:

Selected Sources
Barbette, Paul (1676), Thesaurus Chirurgiae: The Chirurgical & Anatomical Works of Paul Barbette… Together with a Treatise of the Plague… (London).
Scott, Susan and Duncan, C. J. (2001), Biology of Plagues. Evidence from Historical Populations (Cambridge: Cambridge University Press).
Slack, Paul (1990), The Impact of Plague in Tudor and Stuart England (Oxford: Clarendon Press).
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