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Theory of Contagion

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Theories of Contagion

Joseph Du Chesne, Quercetanus redivivus (Frankfurt, 1648), detail from title page.

As Nutton (1983) has pointed out, Galen had indeed written of the possibility of seeds of disease, a view which suggested a belief in the contagious nature of some diseases, in such tracts as On initial causes, On the different types of fever, and in his commentary on the first book of the Epidemics. Galen’s ‘seeds’ were intended to explain why some people contracted a particular disease while others escaped and he located them within the body. Such views were, however, overwhelmed by the scale of his work on the humoral theory of disease, a view based on Aristotle’s four causes which dominated medical debate throughout the medieval and early modern period. Humoral medicine concentrated on the uniqueness of each individual patient rather than on unknowable ‘seeds’ which could not be tracked down by the physician. The focus instead was on rebalancing the four humours of black bile, yellow bile, phlegm and blood which would lead to the patient regaining health. Since each patient had a different constitution the focus was on knowing the patient, not the disease.

Portrait of Girolamo Fracastoro: Courtesy of the National Library of Medicine.

The first dissenting voice came in the sixteenth century when the Italian physician Girolamo Fracastoro (c.1478-1553), wrote his famous De contagion, contagiosis morbis et eorum curatione libri III in April 1546, publishing views which he had already expressed privately to Giovanni Battista della Torre. Worth collected not one but two editions of the works of Fracastoro, collections which included his famous tract of syphilis but which were equally famous for his three-fold view of contagion: by direct contact, indirect contact and at a distance. Contagion by indirect contact was via fomes, substances found in the clothing of diseased people. Seeds of disease which caused contagion at a distance were thought to be stronger than seeds which caused disease by direct contact. The seeds attacked from without, entering the body via the breath or the blood-stream and ultimately led to putrefaction. Fracastoro’s ‘seeds of disease’, seminaria, and his argument that they played a vital role in the development of epidemics might at first look like a radical new departure but as Nutton (1990) has shown, many of his contemporaries, when they paid attention to his views, regarded them not as an attack on Galen, but as an additional commentary on the original ‘seeds’ debate.

Fracastor, in true Renaissance fashion did his best to present his theory of disease as a continuation rather than an innovation of earlier theories, and, as Nutton (1983) points out, there was some truth in this. Certainly his views on contagion and the methods by which it might be contained had been in practice in Italy for some time: as Carmichael’s (1991) work on fifteenth-century Milan has demonstrated, Duke Giangaleazzo Visconti’s (1351-1402) official policy on plague involved strict segregation and quarantine and was evidently based on a theory of human-to-human transmission, a policy which was again implemented by Galeazzo Maria Sforza when plague broke out in Milan in 1468.

As Carmichael (1991) and Kinzelbach (2006) have shown, a crude division between a lay belief in contagion (as evidenced by city state public health policies) and a learned medical over-reliance on miasmatic explanations tied to humoral medicine, is too simplified. Some collegiate physicians in fifteenth-century Milan might not have been supporters of the contagionist underpinning of the public health policy of the ducal regime but the ducal physicians themselves were keen advocates of it. Kinzelbach (2006) points to the seemingly contradictory theories of contagion used by both physicians and laymen and women to explain epidemic disease in the later medieval and early modern German Imperial towns of Augsburg, Nördlingen, Überlingen and Ulm. Likewise, as Nutton (1990) tells us, in the sixteenth-century academic debates about contagion between Giambattista da Monte, professor of practice medicine at Padua, and Fracastoro, the ‘bad air’ theory of the non-contagionists could fit side-by-side with theories of contagion by other means.

The da Monte school in the main tended to ignore Fracastoro’s works but he was by no means a one book wonder: his work ran to a number of editions, possibly due to the outbreak of plague at Venice in 1555-57 when his ideas were revivified. Fracastoro’s reputation improved the further north his ideas travelled, not least because German doctors such as Johann Crato von Crafftheim, physician to the emperors Ferdinand, Maximilian and Rudolf II, spread his ideas in their own writings on plague. There was a certain irony in this for bubonic plague at least was not technically contagious (human-to-human contact) unless it developed into pneumonic plague.

Plague was also the focus of another famous theorist of contagion whose works were collected by Worth: Richard Mead (1673-1754). Worth’s copy of Mead’s A short discourse concerning pestilential contagion (London, 1722) is explored in further detail in the Plague section of this website, but what concerns us here is his theory of contagion – and Mead quite definitely considered plague to be contagious. As Zuckerman (2004) points out, this was true only of pneumonic plague (and haemorrhagic plague) but was not strictly true of bubonic plague where transmission was dependent on rat fleas. Mead was by no means alone in his view though and in the methods of quarantine he advised the English government to adopt in the light of the threat of plague from Marseilles in 1720. Worth’s copy of Mead’s A short discourse concerning pestilential contagion is the eighth edition of 1722. The fact that the text had undergone eight editions in the space of two years attests to its contemporary popularity – as does the fact that it was translated into a number of languages. This may not have been the only reason Worth acquired this volume, for in his eighth edition Mead specifically took issue with the non-contagionist theories of François Chicoyneau, the celebrated French physician at Marseilles whose works were avidly collected by Worth.

Where Chicoyneau (1672-1652) advocated the theory that the principal cause of the Marseilles plague was a combination of bad air and diet, Mead pointed to other factors, factors which, as we have seen, were by no means new but had been recognised throughout the Middle Ages and the early modern period. Fracastoro’s theory of seeds had been prevalent in later works (also collected by Worth), such as Isbrand de Diemerbroeck’s Tractatus de Peste, a work specifically referred to by Mead.

Mead’s unique approach was to investigate plague in the light of smallpox, another contagious disease which also led to characteristics eruptions. He deduced that plague was transmitted by infection from humans, goods and by the air. In his view, it could only be combated by following the Italian model: building lazarettos for quarantine and careful segregation of the sick. All merchandize which had come into contact with sick people had to be burnt. Such strictures (undoubtedly of value) were, however, politically difficult to enforce given their impact on trade and Mead somewhat ameliorated his strictures in the eighth edition. This edition was much expanded and included, among other things, a discussion on Newtonian science which would have made it even more attractive to Worth, given his fascination with this topic.

That plague was certainly considered a contagious disease in the Dublin of Worth’s day may be seen from the following illustration of the Dublin Quarterly Bills of Mortality, in Worth’s copy of Sir William Petty’s Further observation upon the Dublin-bills: or, Accompts of the houses, hearths, baptisms, and burials in that city (London, 1686).

Quaterly Bill of mortality, Dublin, 1681.

Petty, in his postscript to the stationer, tells us that ‘in the Quarterly Bills, we reduce the Diseases to Three Heads, viz. Contagious, Acute, and Chronical; applying this distinction to Parishes, in order to know how the different Scituation, Soil, and way of living in each Parish, doth dispose Men to each of the said Three Species: and in the Weekly Bills we take notice not only of the Plague, but of the other Contagious Diseases in each Part; that strangers and fearful Persons may thereby know how to dispose of themselves.’ Here we see that under ‘Acute Disease’ Petty had ‘Sudden Death, Quinsie, Pleurisie, and Fever’; under ‘Chronical’: ‘Stone, Gout, Dropsy and Consumption’ and under ‘Contagious’: ‘Plague, Smallpox, Spotted Fever and Measles’

Selected Reading
Carmichael, Ann G. (1991), ‘Contagion Theory and Contagion Practice in Fifteenth-Century Milan’, Renaissance Quaterly 44, no 2 (1991), pp 213-256.
Kinzelbach, Annemarie (2006), ‘Infection, Contagion, and Public Health in Late Medieval and Early Modern German Imperial Towns’, Journal of the History of Medicine and Allied Sciences 61, no 3, pp 369-389.
Mead, Richard (1722), A short discourse concerning pestilential contagion (London).
Nutton, Vivian (1983), ‘The Seeds of Disease: An Explanation of Contagion and Infection from the Greeks to the Renaissance’, Medical History 27, pp 1-34.
Nutton, Vivian (1990), ‘The Reception of Fracastoro’s Theory of Contagion: The Seed that fell among thorns?’, Osiris 2nd Series, 6, Renaissance Medical Learning: Evolution of a Tradition, pp 196-234.
Zucherman, Arnold (2004), ‘Plague and Contagionism in Eighteenth-century England: The role of Richard Mead’, Bulletin of the History of Medicine 78, no. 2. Pp 273-308.

Elluchasem Elimithar Tacuini Sanitatis (Strasbourg, 1531), p. 101. 

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