Smallpox in Boston, Massachusetts[1178].
| Population, whites and blacks | Attacked by smallpox | Died of smallpox | Had smallpox before | Moved out of town | ||||||
| 1721 | 10,565 | 5989 | 844 | All the rest less 750 | — | |||||
| 1752 | 15,684 | 5545 | 569 | 5598 | 1843 |
These enormous mortalities in Boston were comparable to those of the old plague itself in European cities, not only in falling upon all ages but also in doubling or trebling for a single year at long intervals the annual average of deaths:
| Deaths of whites | Deaths of blacks | Total | |||||
| 1701 | 146 | — | 146 | ||||
| * | 1702 | 441 | — | 441 | |||
| 1720 | 261 | 68 | 329 | ||||
| * | 1721 | 968 | 134 | 1102 | |||
| 1722 | 240 | 33 | 273 | ||||
| * | 1730 | 740 | 160 | 909 | |||
| 1731 | 318 | 90 | 408 | ||||
| * | 1752 | 893 | 116 | 1009 |
* Smallpox years.
Just as smallpox in its first great outbursts in the London of the Stuarts, or in its rare outbreaks in the American colonies in the 18th century, fell impartially upon children and adults, so in its last outbursts in the London of Victoria it fell upon persons at all ages. The notable thing is, not that smallpox should have of late been attacking adults, for that it has ever done except in times and places in which there were few or no adults who had not been through the disease in childhood; but that it should have ceased to so large an extent to attack infants and children. It has ceased to attack infants and children because other infective and non-infective diseases more appropriate to the modern conditions of the population are attacking them instead. These are measles and whooping-cough, scarlatina and diphtheria, infantile diarrhoea, and the more chronic after-effects of these. The annual death-rate from all diseases under the age of five has fluctuated somewhat per million living from 1837 to the present time, but it can hardly be said that it has fallen much or steadily[1179].
Keeping still to the epidemic of 1871-72, let us consider whether there was any natural or epidemiological reason for its cutting off a smaller ratio of infants and children in its whole mortality than that of 1837-40 did. There had been a most disastrous epidemic of scarlatina for three years just before, which had caused 21,912 deaths in 1868, 27,641 in 1869, and 32,543 in 1870, a total of 82,096 in three years, about two-thirds of which were under the age of five, or at the age-period which smallpox used to be fatal to almost exclusively and to be the greatest single epidemic scourge of. Even in the two smallpox years themselves the scarlatinal deaths were 18,567 and 11,922, of which the share that fell to children under five was one and a half times the deaths in that age-period from the co-existing smallpox. The three years of excessive scarlatina, before the epidemic of smallpox began, had removed large numbers of the class of infants and children who succumb to any infectious disease; if we cannot give the whole rationale of one infection dispossessing or anticipating another, we can at least understand that the earlier and more dominant infection takes off the likely subjects. What scarlatina did egregiously during the three years just before the great explosion of smallpox, it had been doing steadily (along with measles, &c.) throughout a whole generation since the last great sacrifice of infants and children by smallpox in 1837-40. But the fact that scarlatina had in great part dispossessed smallpox among the factors of mortality under the age of five, did not prevent the latter infection from attacking those of the higher ages who were susceptible of it and were at the same time unvexed by any other great epidemic malady proper to their time of life. If the epidemic of smallpox in 1871-72 had cut off as large a ratio under the age of five years as its immediate predecessor in 1837-40 did, its whole mortality would have been about 70,000 more than it actually was. But in no state of the population or of the public health can we suppose that three years of excessive mortality of children by one kind of contagion would be followed immediately by two years of equally special mortality at the same ages by contagion of another kind. It is not only epidemiological science that tells us this, but also common sense—est modus in rebus.
The saving of life by checking the prevalence of smallpox was a favourite rhetorical topic in the 18th century. Voltaire, La Condamine, Bernoulli, Watson, Haygarth and others, were fond of estimating how many thousands of lives might be saved in a year if inoculation were thoroughly carried out. Dr Lettsom, Sir Thomas Bernard and Mr James Neild, who were interested in prison reforms and in whatever else would reduce the prevalence of typhus, reckoned the possible saving of life under that head as almost equal to the possible saving from smallpox[1180]. For typhus there was no artificial means of restraint; it had to decline before natural causes, if it declined at all,—which, indeed, it has done. But no one at that time thought of keeping down smallpox except by the inoculation of itself or of cowpox. The economists and statisticians treated each of these artifices in its turn as a factor having a certain absolute value, which they might use like the a and b of a problem in algebra. This they did, of course, in deference to medical authority. What Bernoulli had worked out for the old inoculation, Duvillard did for the new, in his “Tables showing the Influence of Smallpox on the Mortality of each period of Life, and the Influence that such a preservative as Vaccine may have on the Population and on Longevity[1181].” Malthus fell into the conventional way of thinking when he assumed that smallpox alone among the epidemic checks of population was to be controlled artificially; but he introduced an important new consideration. “For my own part,” he wrote in 1803, “I feel not the slightest doubt, that if the introduction of the cowpox should extirpate the smallpox, and yet the number of marriages continue the same, we shall find a very perceptible difference in the increased mortality of some other diseases[1182].”
Five years after this was written, there came, in 1808, the disastrous epidemic of measles, which in Glasgow killed more infants in a few months than smallpox had ever done at its worst in the same city. In the winter of 1811-12 there was another severe epidemic of measles in Glasgow; and in 1813, Dr Watt, a leading physician of the place, and a man now famous in all countries for his vast labours as a bibliographer, gave to the world his statistical proof, from the Glasgow burial registers, of that law of substitution which Malthus had found necessary in his deduced principles.
“The first thing,” said Watt, “that strikes the mind in surveying the preceding Table (1783-1812), is the vast diminution in the proportion of deaths by the smallpox, a reduction from 19·55 to 3·90. But the increase in the subsequent column [measles] is still more remarkable, an increase from 0·95 to 10·76. In the smallpox we have the deaths reduced to nearly a fifth of what they were twenty-five years ago [in ratio of the deaths from all causes]; in the same period the deaths by measles have increased more than eleven times. This is a fact so striking that I am astonished it has not attracted the notice of older practitioners, who have had it in their power to compare the mortality by measles in former periods with what all of them must have experienced during the last five years[1183].”