Many years after, when the enormous increase of deaths by scarlatina was illustrating the doctrine of displacement in a new way, Dr Farr gave a full analysis of Watt’s essay in his annual Letter to the Registrar-General for the year 1867, and endorsed the Glasgow teaching of 1813 with more heartiness than it had hitherto received. Although Farr did not take the Malthusian view that the loss of weakly children by one means or another was inevitable, yet he could not help seeing, in his work upon the registration returns from 1837 onwards, that one infection had been taking what another spared. He recurred to Watt’s doctrine time after time in his annual reports, and in that of 1872 (p. 224), expressed his belief thus plainly: “The zymotic diseases replace each other; and when one is rooted out, it is apt to be replaced by others which ravage the human race indifferently whenever the conditions of healthy life are wanting. They have this property in common with weeds and other forms of life: as one species recedes, another advances.”
Two remarks remain to be made under the doctrine of displacement. The first is that the substitution of measles for smallpox was one of a series of such changes in the public health of Britain. The great infective scourge of medieval and early modern periods had been plague, which destroyed at times immense numbers of the valuable or mature lives. Its successor was typhus fever, which also cut off the parents more than the children, but did not retard population as the plague had done. The saving of life by the extinction of plague was in great part balanced by the loss from smallpox, which fell, however, more and more upon the earliest years of life until at length it was almost confined to them. The first great decline of smallpox itself corresponded to a great decline of typhus fever during the second half of the French war; but while there was no great infectious disease in those years to thin the ranks of the adults, measles took the place of the more loathsome smallpox in cutting off a certain number of young lives. While the older types of infection have disappeared, the incidence has shifted from mature lives to children, so much so that at the present time enteric fever, and occasional choleras and influenzas, are almost the only infections that correspond to the old plague and to typhus fever in their age-incidence.
The other remark is that the greater prevalence or fatality of measles, as if in lieu of smallpox, meant a good deal more for the bills of mortality than actually appeared under the name of measles. Smallpox was not an infection that did much constitutional damage to those that came through it, although it sometimes destroyed the vision and spoiled the beauty of the face. On the contrary, it was held by many that the general health was better after an attack of smallpox than before; and, if personal experience can justify an opinion, that ought to be my own view of the matter[1221]. But measles is an infection peculiarly apt to leave mischief behind. The bronchial catarrh, which is an integral part of the malady, and is often the cause of death in the second stage of the attack, may so affect weakly children that the respiratory organs are permanently damaged. Tuberculosis of the lungs is apt to follow measles. Some children, again, fall into mesenteric disease after measles, and die tabid, the intestinal catarrh being as dangerous in one way as the bronchial is in another. Another large proportion of the subjects of measles take whooping-cough[1222]. While smallpox did its work summarily, the full effects of measles were longer in being realized. This may in part explain the fact brought out by Watt, that while fewer children died under two years of age, measles being the dominant epidemic disease, there was an increase in the ratio of deaths from all causes between the years of two and five and from five to ten.
Measles in the Period of Statistics.
The history of measles for nearly a generation after the great epidemics of 1808 and 1811-12 is little known. No one in Glasgow continued Watt’s laborious tabulation of the causes of deaths in the numerous burial registers[1223]; nor was any regular account kept elsewhere except by the Parish Clerks of London. The following deaths by measles in their bills from 1813 to 1837, when the modern registration began, were probably no more than from a third to a half of the deaths in all London:
| Year | Measles deaths | |
| 1813 | 550 | |
| 1814 | 817 | |
| 1815 | 711 | |
| 1816 | 1106 | |
| 1817 | 725 | |
| 1818 | 728 | |
| 1819 | 695 | |
| 1820 | 720 | |
| 1821 | 547 | |
| 1822 | 712 | |
| 1823 | 573 | |
| 1824 | 966 | |
| 1825 | 743 | |
| 1826 | 774 | |
| 1827 | 525 | |
| 1828 | 736 | |
| 1829 | 578 | |
| 1830 | 479 | |
| 1831 | 750 | |
| 1832 | 675 | |
| 1833 | 524 | |
| 1834 | 528 | |
| 1835 | 734 | |
| 1836 | 404 | |
| 1837 | 577 |
The inadequacy of these figures to the whole of London will appear from the fact that the registration returns under the new Act gave for the last six months of 1837 the measles deaths at 1354, while the bills of the Parish Clerks gave them at 577 for the whole year. But the old bills enable us to compare the deaths from different diseases within the same area and under the same system of collection, and to compare the deaths “within the bills” in a series of years since the last of the new parishes were taken in about the middle of the 18th century. Using the bills so far legitimately, we find that measles at length came to be of equal importance with smallpox itself as a cause of death in childhood, and that it had become a larger and steadier total from year to year.
So far as concerns Glasgow, the high mortality from 1807 to 1812, making 10·76 on an annual average of the deaths from all causes, was not maintained. When the tabulation of the causes of death was resumed from 1835, the annual average of measles for the five years ending 1839 was found to be only 6 per cent. of the deaths from all causes, the average of smallpox having come back to 5·3 per cent. During that unwholesome period, in which there was much distress among the working class and a great epidemic of typhus, measles and smallpox were dividing the infectious mortality of childhood somewhat equally, the age-incidence of measles being only a little lower than that of smallpox:
Ages of the Fatal Cases of Measles in Glasgow, 1835-39[1224].
| Under one | 1-2 | 2-5 | 5-10 | 10-20 | 20-30 | 30-40 | 40-50 | Total | ||||||||||
| 1835 | 116 | 141 | 121 | 34 | 10 | 4 | — | — | 426 | |||||||||
| 1836 | 86 | 209 | 183 | 38 | 1 | 1 | — | — | 518 | |||||||||
| 1837 | 77 | 133 | 122 | 16 | 2 | 1 | 350 | |||||||||||
| 1838 | 76 | 124 | 161 | 39 | 3 | 1 | 1 | 405 | ||||||||||
| 1839 | 165 | 259 | 275 | 73 | 7 | 2 | 1 | 783 | ||||||||||
| 520 | 866 | 863 | 200 | 23 | 9 | 1 | 1 | 2482 | ||||||||||