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(382) Lessons Learnt from the 1849 and 1854 Epidemics.

The total advance in knowledge of the etiology of cholera derived from the 1849 and 1854 epidemics may be summed up in the words of Dr. Farre, "The final report of the scientific committee proved conclusively the extensive influence of water as a medium for the diffusion of the disease in its fatal forms. The zymotic theory was established, and Dr. Snow's view that the cholera stuff was distributed in all its activity through water was confirmed."

(383) The Cholera of 1866.

In 1866 cholera was again epidemic in England. It had hovered over Europe the previous year. In the autumn of that year, indeed, a few victims of the disease had died in England, and it had been imported into Portsmouth and Southampton. "At Epping in Essex, the Groombridge family, the medical attendant, and a woman who laid out their servant, were killed by cholera in the last days of September and the first days of October." Nevertheless, it was not until July, 1866, that the disease burst in a limited part of the metropolis. Beginning on July 11th, it reached its maximum severity on July 31st, and then its intensity declined; the number of deaths registered in London from cholera was 5,973, from diarrhoea 3,197, and the total number of deaths from cholera in England was 14,378 (1,842 per million), and 17,170 from diarrhoea (1,036 per million). This epidemic was studied with the greatest care by Radcliffe, Parkes, and a number of other well qualified observers, and the reports of Dr. Farre, of Sir John Simon, of Dr. Netten Radcliffe and others on the medical staff of the Local Government Board, are some of the most valuable which have ever appeared upon the subject and will repay perusal.

(384) The East London Water Company and the Cholera of London.

Dr. Radcliffe proved that the area of greatest cholera incidence in London almost exactly coincided with the area supplied by the East London Water Company. The map in which the districts are

shaded according to cholera mortality, of the original report, is very striking, and it would be difficult to convince any reasonable person that so close a coincidence was due to chance; still less so, when the description of the condition of the water-works at that time and other facts are known.

The East London Water Works drew their supply from the river Lea, near Tottenham Mills, certainly not at that point a pure stream, and below it nothing but a sewer receiving the sewage of a large mass of the London population. After depositing in subsidence beds, the water went to a series of filtering beds at Lea Bridge, and from Lea Bridge the water was led by a closed iron conduit to two covered reservoirs on the west bank of the Lea at Old Ford. On the opposite bank were two immense reservoirs, the water of which was when required for use sent along an open foul conduit to the filtering beds at Lea Bridge, but it was possible to turn the water unfiltered from the northern uncovered reservoir into the service covered reservoirs. A careful examination also

proved that all these reservoirs were liable to soakage from the filthy waters of the Lea. The engineer of the Company confessed that at the close of June, or at the beginning of July, unfiltered water was drawn from the northern uncovered reservoir into the covered reservoir to the depth of three inches to supplement a defective supply from the filter beds. It was also proved that the first known cases occurring, in one household June 12th, in another June 26th, got rid of their cholera dejecta undisinfected into drains which went direct into the Lea a little way above the reservoirs. In other words, there was direct evidence of the Lea having been placed under conditions of specific contamination, that this river water could gain access by soakage into the reservoirs, and that one of the reservoirs containing unfiltered Lea water had communicated with the covered service reservoir, and that this water had been drunk by a large population.

It is true there were outbreaks in the same area which did not fit in with this theory, but with regard to these there were possibilities of infection by contact with the discharges of patients either immediately or otherwise, or there was a more or less plausible explanation. On the whole, the water carriage theory was held at that time and is still held to sufficiently explain the epidemic of cholera in 1866 so far as the Metropolis is con

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cerned. This belief was strengthened by the strictly parallel case of Newcastle-on-Tyne. The ordinary death-toll in that city was 11 daily from all causes, but in the height of the cholera epidemic, people were dying from cholera alone at the rate of from 100 to 146 per day. The Tyne Company, running short of water, had pumped in the sewage laden river, polluting their purer supply. The colour of the water is said to have resembled porter. On stopping the drinking of this liquid, and substituting a proper supply, the cholera was stayed.

(385) The Relation of Altitude to Cholera Mortality.

The mathematical relation of altitude of cholera mortality had been deduced by Dr. Farr from the lessons of the epidemic, both of 1849 and 1854, in the following terse rule :-" The mortality of cholera is inversely as the elevation of the people assailed above the sea level," but the deviation from Farr's rule in the 1866 epidemic was very wide if applied to the whole metropolis. The mortality from cholera in the lowest lying districts (under three feet above high water mark) was less than in districts at an elevation of from 3 to 10 feet; the greatest mortality occurred at an altitude of from 10 to 20 feet; the next greatest at from 20 to 40 feet; and the number following in order after this at from 40 to 60 feet." Although the rule did not hold good when applied to the whole Metropolis, it did so in the most affected locality. The numbers in the East and North-East districts being 107, 89, 88, 76, 17, 4, from the lowest elevation up to 60 to 80 feet. Mr. Radcliffe remarked upon this that "it would seem as if a certain degree of intensity of prevalence of cholera in the metropolis is requisite before the mortality follows the law as to elevation unfolded by Dr. Farr."

(386) Mortality of Cholera in Relation to Age and Sex.

According to Farr, the mean mortality in the last three English epidemics was of males 180, of females 178 to 10,000 living of all ages.

"The mean mortality from all causes in the three cholera years was, for males, 19.3 in excess, for females, 17.9 in excess of the

average mortality to 10,000 living; so females suffered less than males.

The mortality is higher in boys than in girls at all the ages under 15; at the ages of reproduction, 25-45, the mortality of women, many of them pregnant, exceeds the mortality of men ; but at the ages after 65 the mortality of men exceeds the mortality of women.

There is evidently a law of mortality involved in the age independently of sex; thus in the three first lustres of life the deaths of boys to 10,000 living were 31-8, 13-2 and 76; of girls 284, 126, 6·4; and the mean mortalities of the two sexes at the same ages were 301, 12.9, and 70, which differ little from the series 301. 145, and 70, where the numbers are obtained by assuming that the mortality is inversely as the age, and decreases about 14 per cent. for every year of age, or is less than half at 5-10, and less than a fourth at 10-15, what it was in the first five years of life.

After the age of puberty, or from the age of 15 to 25, the mortality also increases very little; it is 81 for males and 78 for females; and at the six decennial ages extending from 25 to 85, the mortality increases from 154 to 436, at a very constant rate, as is seen on comparing the calculated series with that observed in both sexes.1

THE DEATHS OBSERVED IN THREE EPIDEMICS BY CHOLERA TO 10,000 LIVING AT EACH AGE.

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Let ma =

mortality by cholera at age x, then rmx=mx+n= mortality at age x + n. In the series given the logarithm of r is taken as 193665. This applies only to the ages under 15. At the ages from 25 to 85, and even upwards, the logarithm of r is 0·00911.

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Thus to 10,000 men living of the age of 25 and under 35 the deaths by cholera and choleraic diarrhoea, as above defined, were 15.2; to 10,000 women the deaths were 156; and the mean mortality of the two sexes in equal numbers is expressed by 154. The mean deaths by cholera at the next age (35-45) were 198 to 10,000 living, and so on. The calculated series approximates very closely to the observed facts: it is a series in geometrical progression and may be conceived as representing this principle that human life loses the power of resisting the zymotic life of the cholera epidemic year by year after the age of puberty, or what is equivalent, that the lethal power of the epidemic on the organism increases at the rate of 2·12 per cent. Thus for instance, 1,000,000 persons of the age of 30 are exposed to cholera, and 1,540 of them die; then of the same number of the age 31 exposed to the same epidemic under exactly the same circumstances 1,573 will die, and to 1,000,000 persons of one year of age older, or age 32, the deaths will be 1,606. So some force is taken away from the organism every year of life, every second we may conceive, by which its constituents become less able to resist the action of the cholera leaven. And the diminution of resisting force obeys a law which is of this nature; the loss is an accumulating quantity, and in the end becomes so great as to leave the life at the mercy of other forms of life or of other forces.

Thus the mortality at one age being given, the mortality at any other age within certain limits can be calculated.1

(387) Symptoms.

Cholera has without doubt a period of incubation, but the difficulty in knowing when the infection first occurred in but a comparatively small number of cases has caused this period to be variously estimated by different writers. The most probable statement is that of Niemeyer, who fixed it at not less than thirty-six hours and not more than three days.2 The symptoms of cholera vary according to severity, the most severe of all killing at once without intestinal discharge-the so-called "cholera sicca"; a less

1

m60 = 730m30 = 28.89

15 407-30 15:40 × (1.0212) 30. By logarithms A15:40 + 30λr = xm60 = A28.89.

2 Farr, Report on the Cholera Epidemic in England, Supplement to Twenty-ninth Annual Report of the Registrar-General. London, 1868.

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