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meets with the fighting descendants of the old heroes, and the attack is immediately repulsed, and this is the nature of protection conferred from a recovery from a first attack. Since it would seem that the weapon of the microbe is its venom, it is not surprising that the macrophages may be educated in their resistance by being dosed with the excretory products of pathogenic organisms; the method of education being first doses feeble in either quantity or strength, to be followed by gradually successive doses of increasing virulence, until no health disturbance is produced by an otherwise mortal dose. The efficacy of ordinary vaccination against smallpox may be explained on the theory that vaccine contains a number of degenerate colonies of the same genus as the smallpox microbe, these are conquered with comparative ease; nevertheless the result is that a race of macrophages are left which, from their education, successfully cope with the virulence of true variola. The remarkable recent investigations of Ferd. Hueppe and Dr. Cartwright Wood, tend to show that even saprophytic bacteria may be used to confer a certain kind of immunity, if they be nearly allied in form, to the pathogenic bacteria, the possible theory being, that the ancestral form of the saprophytic bacteria was pathogenic, but that it has lost nearly all pathogenic properties, save that of splitting up albumen. (See Public Health, Vol. II., 269.)

(278) Classification of Micro-Parasitic Diseases.

At the present time it is impossible to classify micro-parasitic diseases on a scientific basis. All that can be done is to provisionally arrange these diseases into groups for the purpose of convenience, and for this purpose the author proposes the following:-1. Eruptive fevers. 2. Micro-parasitic diseases affecting the nervous system. 3. Micro-parasitic diseases mainly attacking the respiratory passages. 4. Septicæmic maladies. 5. Tubercular. 6. Malaria. 7. Micro-parasitic maladies primarily affecting the intestine. In considering these different maladies, the chief points which concern the sanitarian, are their method of propagation, the period of quarantine necessary, and the suitable means for isolation and disinfection. Properly speaking the medical officer of health still less the sanitary inspector, has little to do with diagnosis, none with treatment, these things being the business of the medical attendant.

CHAPTER XXVI.

ERUPTIVE FEVERS,

SMALL-POX, MEASLES, SCARLET FEVER, AND TYPHUS.

1. Eruptive Fevers.-To this class belong small-pox, chicken-pox scarlet fever, measles, and true typhus.

SMALLPOX.

(279) Incubation and Eruption.

The incubation period averages fourteen days, or, to speak more accurately, twelve days intervene, from the first infection to the symptoms preceding the eruption, on the second day of which spots appears, fourteen days being the general period from infection to actual eruption; if, however, small-pox virus be actually inoculated then the incubation period is shorter, about nine days being considered the average.

The general course of an uncomplicated case of ordinary smallpox, is that the patient feels ill, has high fever, the temperature being 104° or above, there is intense pain in the back, a pain not situated in the muscles, and not particularly aggravated by movement, and usually located in the central part of the sacrum. As with all fevers, the high temperature itself disturbs the nervous centres, children have convulsions, adults are drowsy, dull, or may be delirious. Vomiting is a frequent symptom. The eruption appears in three successive crops, first the head and face, then the body, and lastly the legs. The first appearance of the eruption is that of papules, that is, small red spots about the size of a pin's head, although not at first projecting above the surface. On feeling

the spots there is a sensation of a solid body, and as the eruption farther develops each spot becomes a solid nodule; on either the second or third day of the eruption the spots become vesicular, and of a peculiar shape, for they are flattened at the top, and bound down or umbilicated at the centre; this vesicular stage lasts about four days, it then becomes pustular but the process is gradual, even on the fifth or sixth day, the central part may be vesicular and on puncture yield clear lymph, while the outer part is purulent and on puncture yields matter. When the vesicle becomes wholly purulent the "bride," which bound down the centre of the vesicles, ruptures, and the vesicle, now becomes acuminated, from this stage to the falling off of the scabs, there is most swelling of the face, when the eyelids are closed, and the disease is in its most repulsive stage. About the eighth day of the eruption a dark spot is seen at the centre of each pustule, here the cuticle ruptures and weeps out purulent fluid, which on drying forms a scab. Now is developed the peculiar sickly smell always to be smelt in cases of bad small-pox. From the eleventh to the fourteenth days the crust becomes detached, and the period of convalescence commences. The general period of actual illness being from fourteen to sixteen days, and eighteen after the falling off of the crusts, it will be usually safe to allow the sufferer to return to his avocations. within thirty-two days, precautions to be detailed having first been taken. From the returns of the Asylums Hospital Board, London, it appears that the mean duration of the disease from first eruption to discharge from hospital, in cases returned as "vaccinated," is twenty-five days, the maximum being fifty-five days, the minimum eighteen days, a sufficient number of cases of non-vaccinated cases have not been received to obtain a true average, but it would probably be more than thirty days (the maximum being the same).

The varieties of small-pox are not of the greatest importance to the health officer; thus, when the eruption is composed of vesicles perfectly distinct one from the other it is called "distinct," when the pustules are so thick that they run one into the other it is called "confluent" small-pox; when the vesicle dries up and does not develop into a purulent centre it is the mild form of small-pox known as "horn." The method of prevention is however the same in all, and all must be treated as equal in public danger.

(280) Mortality of Small-pox.

This varies with regard to the vaccinated or unvaccinated state of the individual attacked, with the virulence of the disease itself, and with the general hygienic condition of the patient's surroundings. The latest experience of small-pox in England of any magnitude is the Sheffield outbreak, which was investigated with so much care by Dr. Barry. Of 4,703 cases of small-pox in Sheffield, of all ages of both sexes, and some being vaccinated, others not, 474 died, equal to a mortality of 10 per cent of those actually attacked. Separating these into two general age groups, 581 children under ten years of age attacked, 106 died, giving a mortality of 18.2 per cent.; of 4,096 persons over ten, 368 died, equal to a mortality of 8.9 per cent.

On separating the cases into two groups, vaccinated and unvaccinated, the following were the very remarkable differences recorded:

VACCINATED.

Out of 4,151 cases of all ages 200 died, equal to a case mortality of 4.8 per cent.

Out of 353 cases of children below 10 years of age 6 died, equal to a mortality of 1.7 per cent.

Out of 3,774 cases of persons 10 years of age and upwards 194 died, equal to a mortality of 51 per cent.

UNVACCINATED.

Out of 552 cases of all ages 274 died, equal to a case mortality of 49 6 per cent.

Out of 228 cases of children below 10 years of age 100 died, equal to a case mortality of 43.8 per cent.

Out of 322 cases of persons 10 years of age and upwards 174 died, equal to a mortality of 54 per cent.

So that it may be laid down that the mortality of all ages and both sexes in a vaccinated community will be under 5 per cent. ; in an unvaccinated community it will be over 49 per cent. of those attacked; and if the ratio of the two classes of cases, vaccinated or unvaccinated, be known, the mortality will be in accordance with what may be calculated from the above figures.

(281) Seasonal Prevalence of Small-Pox.

Small-pox has a very definite relation to season; the cases are above the average from Christmas till the end of June, the maximum being about the last week in May, the minimum the

last week in September. The following curve is one based upon mortality returns, from Buchan and Mitchell's paper 1:

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The curve represents the average mortality of thirty years, from 1845 to 1874 inclusive, in London. The straight black line represents the mean weekly average death-rate on an average of the fifty-two weeks; with this the average death-rate of each week is compared, and the difference above or below is calculated in percentages of the mean weekly death-rate for the whole year. Thus the mean weekly death-rate for the year is 19-2; the average of the death-rate for small-pox in the first week was 22, which is 2:8 above the average, or 15 per cent; the average for the first week of October is 13, being 6-2 below the average of fifty-two weeks, or 32 per cent.

Death from small-pox usually takes place from the seventh to to the twelfth day. Hence, although the curve is that of mortality only, it is a fair indication of the number of cases, and a medical officer of health, by watching carefully the progress of small-pox in his district, can with confidence early forecast whether it is likely to become epidemic or not. Thus, if there should be cases in December and January, and these increase in the succeeding months, the probability of an epidemic is strong, whereas smallpox absent during the early months of the year would indicate that there would be no epidemic that particular year.

(282) The Infection of Small-Pox.

The usual spread of small-pox is from person to person, but from inquiries which have taken place as to the influence of small-pox hospitals upon a surrounding population, and the experience of the Sheffield epidemic, it is certain that the infection can strike at a

"The Influence of Weather on Mortality." Journ. of the Scottish Meteorological Society, 1874.

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