The facts are placed clearly before our eyes.

We must, however, bear in mind that this violent disease does not always appear in the same form, and that while the essence of the poison which it produces, and which is separated so abundantly from the body of the patient, remains unchanged, it is proteiform in its varieties, from the almost imperceptible vesicle, unaccompanied by fever, which exists for some time before it extends its poison inwardly, and then excites fever and buboes, to the fatal form in which carbuncular inflammations fall upon the most important viscera.
Such was the form which the plague assumed in the fourteenth century, for the accompanying chest affection which appeared in all the countries whereof we have received any account, cannot, on a comparison with similar and familiar symptoms, be considered as any other than the inflammation of the lungs of modern medicine, a disease which at present only appears sporadically, and, owing to a putrid decomposition of the fluids, is probably combined with hemorrhages from the vessels of the lungs.

Now, as every carbuncle, whether it be cutaneous or internal, generates in abundance the matter of contagion which has given rise to it, so, therefore, must the breath of the affected have been poisonous in this plague, and on this account its power of contagion wonderfully increased; wherefore the opinion appears incontrovertible, that owing to the accumulated numbers of the diseased, not only individual chambers and houses, but whole cities were infected, which, moreover, in the Middle Ages, were, with few exceptions, narrowly built, kept in a filthy state, and surrounded with stagnant ditches.

Flight was, in consequence, of no avail to the timid; for even though they had sedulously avoided all communication with the diseased and the suspected, yet their clothes were saturated with the pestiferous atmosphere, and every inspiration imparted to them the seeds of the destructive malady, which, in the greater number of cases, germinated with but too much fertility.

Add to which, the usual propagation of the plague through clothes, beds, and a thousand other things to which the pestilential poison adheres--a propagation which, from want of caution, must have been infinitely multiplied; and since articles of this kind, removed from the access of air, not only retain the matter of contagion for an indefinite period, but also increase its activity and engender it like a living being, frightful ill- consequences followed for many years after the first fury of the pestilence was past.
The affection of the stomach, often mentioned in vague terms, and occasionally as a vomiting of blood, was doubtless only a subordinate symptom, even if it be admitted that actual hematemesis did occur.