In most instances the region of the earthquake is not specified in the table; but it is sometimes named in the text of the annals under the respective years. Volcanoes are on the whole made more of than earthquakes, Webster’s object being to find evidence of “electrical stimulus,” and not of material miasmata discharged into the air. Etna and Hecla are much in request. Any earthquake suits, as if “earthquake” and “volcano” were like algebraic symbols, always a and b, and never anything but a and b, “influenza” being always x. One begins to realize the difficulties of the volcano or earthquake theory of influenza on turning to Mallet’s Catalogue of Earthquakes[760]. Here, indeed, is an embarrassing choice between China and Peru, Asia Minor and North Africa, Portugal and Sicily or Calabria, Iceland and Jamaica, the Azores and the Philippines, Caracas or Acapulco and Valparaiso, Hungary and Savoy, Kamtschatka and Amboina; between earthquakes great and small; between earthquakes and volcanoes. Any influenza year might be suited with one or more earthquakes, perhaps in either Hemisphere; but there are some long clear intervals between the greater influenzas in Europe, for example the interval from 1803 to 1831, which seem to occupy as many pages of the catalogue of earthquakes as the years wherein influenzas came thickest, for example from 1729 to 1743, or from 1831 to 1847.
None the less, Webster, like Boyle, obeyed a true impulse when he looked for the cause of influenzas in something telluric, occasional, phenomenal. A wave of influenza comes up unexpectedly from a particular point of the compass, passes quickly over many degrees of latitude and longitude, lasting a few weeks at any given place, disappears in the distance, and does not return again perhaps for a whole generation. Influenza has the qualities of suddenness, swiftness, transitoriness; it has a certain sameness in its symptoms; it can be identified as certainly in the brief phrases of medieval chronicles as in elaborate modern descriptions; it has had no season for its own, as plague and cholera have had the summer and autumn, but has reached a height in Europe sometimes in midsummer, sometimes in midwinter. No other epidemic malady can compare with it in these respects; all the rest seem to have been provoked more or less by the turns and changes in human affairs, some being of a medieval colour, others of a modern, each in its own way admitting of explanation from unwholesome living, or from famine, or from over-population, or from something more recondite but still within the sphere of things insanitary in an intelligible sense. Other plagues besides influenza were, it is true, once reckoned mysterious, or associated in the popular mind with earthquakes and comets. But several such plagues have disappeared from among us, while their alleged causes, the earthquakes or comets, continue as before. Influenza alone returns at intervals as of old, untouched by civilization, by sanitation, by the immense differences between medieval and modern, making the same impression upon England in the year 1890 as it did in 1173, or 1427, or 1580, or, if changed at all, then changed for the worse inasmuch as the epidemic came back more severely in 1891, and still more severely in 1892. It is not surprising that for such a disease something telluric or even cosmic should have been assigned as the cause, something as occasional as itself, phenomenal, if not cataclysmic. It may be proper, therefore, that we should try over again the philosophic generalities of Boyle, Arbuthnot and Webster, peradventure a combination of them may yield a true theory. From Boyle we may take the great principle of a progressive infection through regions of air (or leagues of ground), which was expressed once for all by Lucretius in the sixth book of the ‘De Rerum Natura’:
... atque aer inimicus serpere coepit;
Ut nebula ac nubes paulatim repit, et omne
Qua graditur, conturbat et immutare coactat;
Fit quoque ut in nostrum quum venit denique coelum
Corrumpat reddatque sui simile atque alienum.
From Arbuthnot we may take the organic source and nature of the influenzal miasmata, and the association with changes in the level of the water in the soil. From Webster we may take the idea that the historic influenzas, having been sudden, occasional or phenomenal, must have had phenomenal causes somewhere in either Hemisphere. Instead of sketching a theory in the abstract, and safeguarding it by following all its ramifications, I shall proceed by the way of instances, choosing them so as to bring out particular points in order.
The only generality which may be indicated at starting is one that has presented itself time after time in the foregoing history, namely that there is something more than accident in the association between epidemics of influenza and epidemics of ague. So close was this association in former times that both the influenza and the widely prevalent ague were included together under such names as “the new ague,” “the new fever,” “the new distemper.” As late as 1679, Morley did not distinguish the epidemic of influenza from the epidemic agues in the midst of which it was set, although the distinction was real, and was actually made by Sydenham on that occasion, as it had been made by Willis and in a manner by Whitmore on the occasion immediately preceding, and as it was made by everyone on the last great occasion when an influenza made an interlude among epidemic agues in the year 1782. It has often been suspected that influenza was related to some other infection: at one time it was taken for a volatile emanation of plague, in our own time it has been regarded as a volatile emanation of Asiatic cholera. In a wider historical view the question may arise, whether the real relation is not rather to those remarkable agues which have been epidemic in company with influenza when there was no plague and no cholera.
I come now to certain influenzas, as illustrating particular points of theory, in order.
I.
It is probable that Webster’s theory of influenza as related to earthquakes and volcanoes, first published in 1799, was suggested to him by a communication to the Royal Society on the volcanic waves seen at Barbados on the 31st of March, 1761, and on the epidemic of influenza thereafter ensuing all over the island. At Bridgetown, in the afternoon of the 31st of March, 1761, the water in the bay and harbour ebbed and flowed to the extent of eighteen inches or two feet at intervals of eight minutes, and continued to do so for the space of three hours, the oscillation regularly decreasing till night when it was no more observable. These tidal waves were due to volcanic upheavals somewhere; and it was found that the centre of disturbance had been in the Atlantic near the coast of Portugal, and the time some hours earlier than the waves were felt at Bridgetown. The Barbados chronicler proceeds:
“It is very remarkable that since that time the island has been in a very deplorable condition, having suffered under the severest colds that have been ever known. The distress has been so general that I may venture to assert (with confidence) that nineteen twentieths of the inhabitants of the island have felt the effects of the contagion; and to some it has been repeated several times. It has puzzled all the adepts in pharmacy to find out the cause and cure of it. One favourable circumstance has attended it, viz. few have died with it. The Leeward Islands have not escaped, it having raged there more violently and more fatal. His Majesty’s ships have severely felt the effects of it, some of them not being capable of keeping the seas for want of men fit for service. This happening at a season of the year remarkably the healthiest, makes it the more surprising[761].”
This is as good an instance as we shall find, of explaining something sudden, swift, and phenomenal, by something else sudden, swift, and phenomenal, in a purely empirical way and without pausing to ask whether the latter could have been a vera causa of the former. That the influenza came to Barbados in the wake, as it were, of the volcanic waves, had been a common subject of talk among the residents; and that common opinion of the colony had found expression in the paper sent to the Royal Society. The influenza was not only in Barbados, in the Leeward Islands, and in the ships on the West Indian Station, but also in New England and “over the whole country” of the North American Colonies. Dr Tufts, of Weymouth, New England, wrote to Webster that “it began in April, and in May ran into a malignant fever which proved fatal to aged persons. It spread over the whole country and the West India Islands[762].” It was not until some nine months after that influenza appeared in Europe, at first in the east of that continent,—Hungary, Vienna, Breslau, Copenhagen—in February and March, 1762, in central Germany and Scotland in April, in London about the first of May and all over England and Ireland thereafter, but not in France until June and July.