The Black Death

But though the rat helps greatly in the spread of bubonic plague, Professor Jorge is right in his contention that it is not essential. The Plague Research Commission of 1910 commented ‘…the transference of infected rats and fleas in merchandise, or in the case of fleas, on the body of a human being, must be considered.’^{38} It has been, and Dr Hirst has shown that the adage ‘No ship rats, no plague’ is palpably untrue.^{39} X. cheopsis, in ideal conditions, can live for a month away from its host. Travelling with a cargo of grain or in a bale of cloth it could easily journey hundreds of miles without a rat. There is one substantiated case of a flea surviving unfed for six months in a rat burrow. The absence of rats, therefore, was far from a guarantee that bubonic plague could never strike.

The symptoms of bubonic plague as known today coincide precisely with those described by the medieval chroniclers. The ‘swollen and dropsical mass of inflamed lymphatic glands’ known as the bubo is the classic sign. Sometimes this is the size of an almond, sometimes of an orange; usually it is found in the groin but it may also grow in the armpit or, occasionally, on the neck. Equally familiar are the dusky stains or blotches caused by subcutaneous haemorrhages and the intoxication of the nervous system: ‘In Provence a man climbed on to the roof of his house and threw down the tiles into the street. Another executed a mad, grotesque dance on the roof…’^{40} Modern medical experience suggests that, if the bubo breaks down and suppurates within a week, the victim will probably survive; few medieval doctors would have expected their patient to endure more than four or five days of the agonizing pain which accompanies the boil. But otherwise the cases observed by Boccaccio or Simon of Covino could be found in half a dozen plague centres today.

But though bubonic plague was the first and most conspicuous form taken by the Black Death, a variant known as primary pneumonic or pulmonary plague was more lethal. In the epidemics of the late nineteenth century, when methods of treatment were remarkably little more sophisticated than in the Middle Ages, between sixty and ninety per cent of those who caught bubonic plague could expect to die. In the case of pneumonic plague recovery was virtually unknown. Bubonic plague would generally take between four days and a week to kill; in the Manchurian epidemic of 1921 the expectation of life of the victims of pneumonic plague was a mere 1.8 days. Finally, bubonic plague is one of the less infectious epidemic diseases; the breath is not affected and the patient usually died or recovered before enough bacilli have accumulated in the blood to make it a source of infective material for the flea.^{41} Pneumonic plague is perhaps the most infectious; it attacks the lungs so that there is coughing of blood and the plague bacilli are sprayed out into the air every time that the patient exhales.

Hirst has remarked^{42} that, if it were not known that they had a common origin and were linked by intermediate types, true pneumonic and uncomplicated bubonic plague would seem to be different diseases. The link between the two is to be found in an attack of bubonic plague during which the victim also develops pneumonia. This compound, though extremely dangerous to the victim, is not usually infectious. Yet, in certain cases, it may become so. The main outstanding problem of the Black Death, or indeed of the plague in any era, is what the factors are which make this happen, what it is which provokes an epidemic of the air-borne pneumonic variant of the disease.

‘Where the fourteenth-century plague is said to differ from later experience is that in its quite slow extension across Europe it seemed to change as the season of the year changed from pneumonic to bubonic, and then from bubonic to pneumonic without discontinuity’^{43} The medieval doctor can hardly be blamed for finding the process incomprehensible. But if he had understood it he would even then not have mastered the full story. For there would still have remained unexplained those cases, already mentioned, in which a man would die within a few hours or go to bed in the best of health and never wake in the morning.