CHAPTER XLIV.

ACUTE INFECTIVE DISEASES.

Acute Infectious Diseases are characterised by certain definite characters.

1.—_They are usually infectious or contagious._ It is preferable to use these two terms as interchangeable. The modes in which infection is received vary greatly with different fevers.

(1) Some can only be propagated by _inoculation_—the introduction through an abraded surface of a minute quantity of the poison; as in glanders and hydrophobia. Others, again, _may_ be introduced in this way, but are usually acquired in another manner, as scarlet fever, small-pox.

(2) Some are carried through the _atmosphere_. The contagium of small-pox can be carried as far as any, while that of typhus fever only traverses a few feet. The atmosphere acts as a conveyer of infection, and the infectious matter must necessarily, in most instances, be in the condition of dust to enable it to be wafted by currents of air or disturbed by the movements of persons in an infected room.

(3) _Clothes_, books, and furniture are not uncommonly carriers of infection. An old letter, or a lock of hair, has even after many years’ concealment in an enclosed space produced infection on being brought to light. Woollen articles convey infection more easily than calico, and dark clothes better than light coloured. A fever nurse’s clothes should never be woollen, but some washable material.

(4) _Drinking water and food_ often form a vehicle for infection. Milk and water are the two usual sources of infection; but uncooked food, especially oysters and mussels, fed in sewage-polluted estuaries, may produce the same effect. Cholera, enteric fever, dysentery, and summer diarrhœa are the chief diseases from this source; but scarlet fever and diphtheria occasionally have a similar origin. Milk may be infected from having been handed by an infectious patient; or it may possibly convey infection of the disease from which the cow at the time is suffering, _e.g._, tuberculosis (see also page 312). Water may be contaminated with sewage or the excreta of a single infectious patient.

2. _They retain their specific character and origin._ Small-pox never produces scarlet fever, nor _vice versâ_; and it is found universally that all the specific fevers “breed true,” each one retaining its identity. More than this, a previous case of the same fever can nearly always be detected on careful examination. Overcrowding and other insanitary conditions diminish the resistance to infection, and may increase its virulence.

3. _The behaviour of contagia_, when received into the system, is characteristic of these diseases. There is first of all a period of latency or _incubation_, during which no symptoms are manifested (see page 287.) The incubation period is followed by the characteristic symptoms of the particular fever, which disappear in a variable period, leaving the patient, as a rule, more or less _insusceptible to a second attack_ (see page 288).

Throughout the progress of the disease, except in the period of incubation, the patient is able to communicate his disease to persons about him who have not been rendered safe by a previous attack. The way in which he thus communicates his disease varies in different cases. In scarlet fever, the throat and skin are the chief sources of contagion; in influenza, whooping-cough, and measles, the secretions from the respiratory passages; in hydrophobia, the saliva; in enteric fever and cholera, the vomit and stools.

=Prevention of the Spread of the Chief Acute Infectious Diseases.=—We may divide these into three classes. (1) Those which are infectious by contact with the patient or by the atmosphere around him. (2) Those in which the intestinal and renal evacuations are almost alone infectious; as enteric fever and cholera. (3) Those in which inoculation through an abraded surface is generally if not always necessary to produce infection.

SMALL-POX OR VARIOLA.

The contagium of small-pox is very tenacious of life. All parts of the body, and all secretions and excretions contain it. As in typhus it adheres to every article in the room, but unlike typhus is possessed of great vitality, and if not exposed to the air may be active after many years. There is considerable evidence indicating that the contagion of small-pox may occasionally be _conveyed aerially_ for a considerable distance, for even a quarter or half a mile from hospitals in which small-pox patients are isolated. Whether this is the aerial convection of infection, or in part at least due to carelessness of persons connected with the hospital in their movements to and fro, may remain an open question; but such hospitals in the midst of towns are in practice a mistake; and in London small-pox has been found to be more manageable since its small-pox patients were all conveyed to extra-urban hospitals. The means for the prevention of small-pox are (1) Isolation of infectious patients. (2) Disinfection of all infected articles. For particulars under these two heads, see pages 319 and 324. They must be carried out most rigidly in this disease. (3) Vaccination and re-vaccination.

=Inoculation of small-pox= virus was largely practised as a means of ensuring a comparatively mild attack, until it was made illegal in 1840. Sometimes, however, the attack thus produced was fatal, and every case of inoculated small-pox became a new focus of infection, and a source of high mortality, especially among young children.

=Vaccination.= About the year 1795 Dr. Edward Jenner was informed by a milk-maid that she could not take small-pox, as she had already contracted the natural cow-pox during milking. Many had previously heard this same statement made; but Jenner was the first to put the matter to the test. He took the lymph or virus from a woman who had accidentally acquired cow-pox (vaccinia) from a cow, and inoculated a boy with it. Some months later he inoculated the same boy with small-pox, and a second time five years afterwards, without producing small-pox on either occasion. Many other experiments were made, all confirming these results; and in 1798 Jenner published his results.

The practice of vaccination gradually became more general, and was followed by a progressive decrease in the mortality from small-pox.

Cow-pox or vaccinia is small-pox modified and mitigated by its passage through the system of the cow, and not a spontaneous disease of the cow. By its passage through the cow it has become attenuated and altered. Instead of a general eruption all over the body, there are vesicles only at the point of inoculation; and vaccinia, unlike small-pox, is not communicable from person to person except by inoculation. Furthermore it is in the vast majority of instances an extremely mild ailment, not involving more than a few days discomfort.

Objection is taken to vaccination for small-pox on the ground that serious diseases such as syphilis, erysipelas, and tuberculosis may be inoculated at the same time. With lymph obtained from healthy children this is impossible. Most of the cases of infection described have been in reality hereditary disease, the local irritation of vaccination serving to call into activity the morbid tendencies of the child. The risk of such infection is infinitesimal; it may be reduced to zero by moderate care and attention to detail. With modern antiseptic methods, it is very rare for a vaccination sore to “go wrong.” Erysipelas may be inoculated from dirt getting into a vaccination sore, as it may be into any other sore; but with cleanliness this need not occur; and in fact very seldom does occur. The risks are so small as to be negligible; and if the protection afforded is one tithe of what is claimed for it, no parent is justified in withholding this protection from his infant. The _law as to vaccination_ requires that every infant shall be vaccinated within six months of its birth, domiciliary visits for this purpose being made by the public vaccinator. The obligation can only be avoided by a statement on oath before a magistrate by the parent of conscientious objection to vaccination.

=Does Vaccination protect against Small-Pox?= The registration of deaths for the whole country only began in 1837, and before this period death-rates from small-pox in terms of the population cannot be accurately stated. Since that time there has been less or more vaccination, so that it is difficult to obtain a true comparison between periods with and without vaccination. Some indication of the facts in London prior to 1801, when the first English census was taken, may be obtained from the fact that in 1796 (two years before the date of Jenner’s “Inquiry,”) small-pox reached its highest point, causing 18½ deaths out of every 100 total deaths from all causes. In the præ-vaccination period small-pox was 9 times as fatal as measles, and 7½ times as fatal as whooping-cough (McVail), while since vaccination has been practised it has sunk to an insignificant position, when compared with these diseases. Dr. Guy found that in London there were in 48 years of the seventeenth century ten epidemics, in the whole of the eighteenth century 19 epidemics, and in the nineteenth century no epidemic during which the deaths from small-pox caused one-tenth or more than one-tenth of the total deaths from all causes in any year. The worst year under obligatory vaccination in London was 1871, in which barely 4½ per cent. of the total deaths was due to small-pox, a proportion which was exceeded in the eighteenth century ninety-three times.

In Sweden, the highest death-rate _before vaccination_ (1774-1800) was 7·23 per 1,000 inhabitants, the lowest 0·31; under _permissive vaccination_ (1801-1815) the highest 2·57 per 1,000 inhabitants, the lowest 0·12; under _compulsory vaccination_ (1816-85) the highest 0·94 per 1,000 inhabitants, the lowest 0·0005. It has been stated that these results, which might be extended by quotations from the statistics of other countries, have been obtained not by vaccination, but by improved sanitation, including in this term not only improved housing and better water and food supply but also increased means of isolating the infectious sick. Improved housing may by diminishing overcrowding aid in diminishing the spread of this disease. Whether in view of the immense increase in the proportion of the population which lives in towns, it can be said that this has occurred is doubtful. Hospital isolation undoubtedly prevents the spread of infection when promptly effected. But a large share of the improvement in small-pox mortality occurred before either hospital or home-isolation of small-pox patients was generally enforced. There is no reason for supposing that impure water or food, or nuisances about houses have any connection with the origin or spread of small-pox, any more than they have with the origin or spread of measles or whooping-cough; which still remain as prevalent as in the past. Further light can be thrown on the subject by an examination of the age-incidence of small-pox, and of its attack-rate and severity in vaccinated and unvaccinated respectively.

The =age incidence of deaths from small-pox= has, since 1847, when returns classified according to age became available, undergone a remarkable alteration. Prior to 1870 the small-pox deaths in infants nearly always formed 20 per cent. or more of the total mortality from this disease, between 1870 and 1890 they did not greatly exceed 10 per cent. of the total, while since 1890 they have again begun to form an increasing proportion of the total small-pox mortality. At ages 1-5 the change is even more remarkable. Before 1870 deaths at these ages nearly always exceeded 30 per cent. of the total; since 1870 they have varied between 5 and 14 per cent. of the total; and since 1890 they have, like the proportion of deaths under one, again increased. At the higher ages the proportion of deaths has correspondingly increased, so that the curves of age incidence have become curiously inverted.

The lowered birth-rate can only account for a small portion of this transference of the chief mortality due to small-pox from childhood to adult life.

Furthermore it must not be supposed that the only change which has occurred is that the deaths which formerly occurred in childhood now occur in adult life. The death-rate at all ages has greatly declined. The only explanation which in my judgment satisfactorily explains this remarkable change in age-incidence of small-pox mortality is the fact that vaccination protects children from small-pox and that the protection diminishes, though it never entirely disappears, with advancing years. This conclusion is confirmed by the evidence obtained as to the proportion of vaccinated and unvaccinated attacked, and as to the severity of the attacks occurring when a community is invaded by small-pox.

=Attack-rate among Vaccinated.=—If the protective effect of vaccination, like that of a preceding attack of small-pox, wears off, it will not be expected that no attacks of small-pox will occur among the vaccinated. For evidence of immunity from attacks we must examine the records as to =revaccinated= persons exposed to infection. During the six years 1890-95, out of a staff in the London small-pox hospitals varying from 64 to 320, the percentage attacked by small-pox was _nil_, except in 1892 when it was 1·4, and in 1893 when it was 1·9.

Taking the experience of towns in which during recent years epidemics of small-pox have occurred, the following attack-rates have occurred. By attack-rate is meant the percentage number of attacks occurring among persons living in infected houses. By fatality is meant the number dying out of 100 attacked.

┌────────────┬───────────────────────────┬──────────────────────────┐ │ │ ATTACK RATE UNDER │ ATTACK RATE OVER │ │ │ 10 YEARS OF AGE. │ 10 YEARS OF AGE. │ │ ├───────────┬───────────────┼───────────┬──────────────┤ │ │VACCINATED.│ UNVACCINATED. │VACCINATED.│ UNVACCINATED.│ ├────────────┼───────────┼───────────────┼───────────┼──────────────┤ │_Dewsbury_ │ 10·2 │ 50·8 │ 27·7 │ 53·4 │ │_Leicester_ │ 2·5 │ 35·3 │ 22·2 │ 47·6 │ │_Gloucester_│ 8·8 │ 46·3 │ 32·2 │ 50·0 │ └────────────┴───────────┴───────────────┴───────────┴──────────────┘

=Severity (Fatality) among Vaccinated.=—The experience of the same three towns comes out as follows:—

┌────────────┬───────────────────────────┬──────────────────────────┐ │ │ ATTACK RATE UNDER │ ATTACK RATE OVER │ │ │ 10 YEARS OF AGE. │ 10 YEARS OF AGE. │ │ ├───────────┬───────────────┼───────────┬──────────────┤ │ │VACCINATED.│ UNVACCINATED. │VACCINATED.│ UNVACCINATED.│ ├────────────┼───────────┼───────────────┼───────────┼──────────────┤ │_Dewsbury_ │ 2·2 │ 32·1 │ 2.6 │ 18·7 │ │_Leicester_ │ 0.0 │ 14·0 │ 1.0 │ 7·8 │ │_Gloucester_│ 3·8 │ 41·0 │ 10·0 │ 39·7 │ └────────────┴───────────┴───────────────┴───────────┴──────────────┘

In view of such results as the above it is not surprising that the Royal Commission, in their majority report, summed up the advantages of vaccination as follows:

“(1) That it diminishes the liability to be attacked by the disease.

“(2) That it modifies the character of the disease, and renders it (_a_) less fatal, and (_b_) of a milder or less severe type.

“(3) That the protection it affords against attacks of the disease is greatest during the years immediately succeeding the operation of vaccination. It is impossible to fix with precision the length of this period of highest protection. Though not in all cases the same, if a period is to be fixed, it might, we think, fairly be said to cover in general a period of nine or ten years.

“(4) That after the lapse of the period of highest protective potency, the efficacy of vaccination to protect against attack rapidly diminishes, but that it is still considerable in the next quinquennium, and possibly never altogether ceases.

“(5) That its power to modify the character of the disease is also greatest in the period in which its power to protect from attack is greatest, but that its power thus to modify the disease does not diminish as rapidly as its protective influence against attacks, and its efficacy during the later periods of life to modify the disease is still very considerable.

“(6) That re-vaccination restores the protection which lapse of time has diminished, but the evidence shows that this protection again diminishes, and that, to ensure the highest degree of protection which vaccination can give, the operation should be at intervals repeated.

“(7) That the beneficial effects of vaccination are most experienced by those in whose case it has been most thorough. We think it may fairly be concluded that where the vaccine matter is inserted in three or four places, it is more effectual than when introduced into one or two places only—and that if the vaccination marks are of an area of half a square inch, they indicate a better state of protection than if their area be at all considerably below this.”

SCARLET FEVER.

Scarlet Fever and Scarlatina are the same disease. It is extremely infectious, the contagium retaining its virulence for protracted periods. It occurs in epidemics at irregular intervals. During recent years the type of scarlet fever has become greatly attenuated, and this constitutes one of the difficulties of prevention, as the mild form of the disease is apt to be overlooked. The _fatality_ per 100 persons attacked varies greatly with age. It is highest in children under four, rapidly declining with increasing age. Hence the importance of protecting children from attack in early life. Two results follow from the wise precautions taken to prevent attack early in life. (_a_) With each successive year of life the liability to attack, when exposed to infection, diminishes; (_b_) the danger of the attack if it occurs and its liability to be fatal becomes rapidly less with greater age. The most common _mode of infection_ is by contact with a previous patient. Outbreaks due to milk infected by a scarlatinal patient also occur. Infected cream has also been known to convey infection. In a milk outbreak the patients would be found chiefly among the customers of a special dairyman, the cases occur almost simultaneously, except secondary cases which may be infected from the first. The _simultaneous_ occurrence of two or more attacks in one house, especially if the same thing happens in a number of houses should throw suspicion on the milk supply. It has been suggested that scarlet fever may originate apart from human infection, from a special disease of the cow, but the evidence on this point is inconclusive.

The _duration of infection_ is usually reckoned until the desquamation of the skin is complete, _i.e._ about six or seven weeks from the onset of the attack. Occasionally it is more protracted even though desquamation is complete, infection appearing to persist in discharges from the nose and ear and in sore places inside the nostril and possibly in other parts. The period of greatest infectivity is in the earlier part of the disease, when the throat is inflamed. The common notion that the disease is most infectious during the later period, that of desquamation, is erroneous. The micro-organism causing scarlet fever has not certainly been identified. The measures of prevention are those common to infectious diseases (page 317).

MEASLES.

Measles is an extremely infectious disease, before as well as after the rash appears on the fourth day of the disease. The infectivity of the catarrhal stage constitutes one of the main difficulties in preventing its spread, as measles may be unrecognisable at this stage. The common notion that measles and whooping-cough are comparatively harmless infantile complaints will be dissipated by a study of the comparative death-rate for the five years 1891-5 per million persons living in England and Wales:—

ENGLAND AND WALES.—DEATH RATES PER MILLION OF POPULATION.

_Small-pox_ 20 _Measles_ 408 _Scarlet fever_ 183 _Typhus fever_ 4 _Enteric fever_ 174 _Whooping-cough_ 398 _Diphtheria_ 253 _Diarrhœa_ 630

It is a mistake also to suppose that measles and whooping-cough are only serious when neglected. Such neglect greatly increases the likelihood of death from bronchitis or pneumonia; but the diseases themselves, especially measles, are frequently fatal during the acute early stage. More children are attacked with measles under the age of five than at any other age, and the greatest number between two and four years of age. The greatest fatality is in the second year of life, when it may be 24 per cent. of those attacked, as compared with between two and three per cent. in the fourth year of life, and a trifling amount at higher ages. These facts explain the folly of allowing children to have an infectious complaint when another child in the house is attacked, “to have it over at one trouble.” Such action is pregnant with evil results. (1st) Severe cases occur, in which a fatal result ensues; and even where death does not occur, the child may be left weakly and very prone to become tuberculous. (2nd) Every additional case forms a new centre of infection. It is like the old practice of inoculation for small-pox; the individual is protected, but becomes a source of danger to all around him. If there is only one case of measles in a family the risk to neighbouring households is much smaller than where several children are infected. (3rd) Every year that a child’s attack can be delayed, increases his chance of recovery if he is subsequently attacked, and diminishes the likelihood of his being attacked.

The _duration of infection_ should be reckoned as at least three weeks. The contagium of measles does not appear to hang about rooms with the persistence of that of scarlet fever, and less stringent disinfection is required.

WHOOPING COUGH.

Very few people have reached adult life without having suffered from this disease, as well as measles. This is chiefly due to the carelessness in mixing infected with healthy children. One frequently hears the peculiar and characteristic cough of a child with whooping-cough, in public assemblies, in railway trains, or in the out-patient rooms of hospitals. The contagium of whooping-cough is conveyed chiefly by the expectoration, which becoming dry, may be scattered like that of phthisis, as dust. Clothing conveys infection easily; visits to infected children should, therefore, be prohibited to all who have to mix with susceptible children.

The _duration of infection_ should be reckoned as at least six weeks from the first recognisable symptoms. It may be longer than this.

DIPHTHERIA.

This disease has become increasingly prevalent in the last ten years after a period of only slight prevalence for about twenty-five years. I have shown that epidemics of diphtheria occur during a succession of years of protracted drought. Diphtheria is more common in girls than boys, possibly owing to their more affectionate habits; and occurs chiefly under ten years of age, the fifth year of life being that of greatest prevalence. Unlike the acute infections hitherto considered, the bacillus causing diphtheria has been identified and cultivated in the laboratory (called the Klebs-Loeffler bacillus or diphtheria bacillus). Direct infection from patient to patient is probably more common than indirect infection by clothes, etc., though the latter occurs. The infection may hang persistently about a house and its belongings, in the absence of complete purification. When diphtheria is prevalent slighter sore throats occur, sometimes before true diphtheria is detected. This led to the theory that under conditions of overcrowding, especially in schools, there occurred in the micro-organisms causing these sore-throats “the progressive development of the property of infectiveness.” Possibly these were slight non-typical attacks of diphtheria. Such attacks occur also during epidemics of diphtheria, and unless specimens (“throat swabs”) from these sore-throats are examined bacteriologically, are likely to spread diphtheria by attendance at school, etc. Aggregation in schools seems to intensify the contagium of diphtheria. The practices of kissing, of transferring sweetmeats from mouth to mouth, of cleaning slates with saliva, are common means of spreading it. Effluvia from foul drains and sewers have been commonly held to cause diphtheria. If they aid in producing it, it is rather by lowering the vitality and causing ordinary sore throat. Sore throats and catarrhs make the subjects of them much more prone to diphtheria (see also page 117). Damp houses have been stated to favour the development of diphtheria. Probably they do so in the same way as effluvia from drains. It is likely that the diphtheria bacillus has a saprophytic stage of existence in the soil, as indicated by its excessive prevalence in dry warm years. Besides direct infection from patient to patient and indirect infection by _fomites_ (_i.e._ in clothing, etc.), milk occasionally causes epidemics of diphtheria. The infection has been usually caused by the handling of the milk by an infectious person. In certain outbreaks no human contamination of the milk could be discovered; and it has been surmised that an analogous disease in the cow may cause diphtheria in man. This is still a moot point. Fowls, cats, and other animals are the occasional victims of diphtheria, and may convey it to man.

The _duration of infection_ in diphtheria is usually less than six weeks; but it may be much more protracted. In some instances long after all naked-eye evidences of diphtheria has disappeared, bacteriological examination may still show the presence of the diphtheria bacillus for two or three months; in rare cases even longer. The protection afforded by one attack of diphtheria against a second is slight and only temporary. The _means of prevention_ are isolation and disinfection as for other infectious diseases. Two additional means are available (_a_) _bacteriological diagnosis_; (_b_) prophylactic injection of antitoxic serum. Many sore throats without membrane on the throat are due to the diphtheria bacillus. Even if membrane be present there may be doubt as to whether the case is true diphtheria. Hence the importance of bacteriological examination.

The patient’s throat is swabbed with cotton-wool which has been rolled around a metal probe and sterilised. The wool is then smeared over sterilised and solified blood serum in a test tube. It is then incubated over night at a temperature of 37° C. Next morning the minute growth that has occurred on the surface of the blood serum is spread on a microscopic cover-glass, appropriately stained, and examined microscopically. If diphtheria bacilli are present, they can be recognised by their form and arrangement. The same means enable us to ascertain when a patient has recovered, whether he is fit to be released from isolation.

_Antitoxic serum_ has been found to be a valuable prophylactic and curative agent.

The serum is obtained as follows: Sterilised broth is inoculated with virulent diphtheria bacilli, and grown at 37° C. for a week or more. The broth is then filtered through a Pasteur filter. The filtrate contains _toxine_ free from bacilli. Some of this toxine is injected under the skin of a horse. A few days later the dose is repeated, gradually increasing amounts being injected until injection of further quantities of the toxine is found experimentally not to increase the antitoxic value of the horse’s blood serum. Next the horse is bled. Its serum is found to have acquired the power of protecting a guinea-pig against doses of the toxine of diphtheria which would otherwise be fatal. Ten times the quantity of the horse’s serum which will protect a guinea-pig (of 250 grammes weight) against ten times the minimum fatal dose of the toxine is called an antitoxic unit.

The treatment of diphtheria in man by the antitoxic serum thus obtained has proved to be remarkably successful. Furthermore, if a susceptible person who has been exposed to the infection of diphtheria, is injected with a small dose of antitoxic serum, he becomes temporarily immune, and does not fall a victim to diphtheria. This is a most important point especially for young children, who may already be incubating a disease which but for this prophylactic injection might occur and prove fatal.

TYPHUS FEVER.

This disease was formerly known as spotted or jail-fever, and for many ages has been the scourge of prisons and armies, and all collections of people living in overcrowded and insanitary districts. The history of typhus is the history of human misery. It is essentially associated with filth, overcrowding, and destitution; but when once established by these conditions, it can be carried by infection to others who live amidst healthy surroundings. It generally occurs in winter, when overcrowding is greatest. With free ventilation, the disease cannot be carried more than a few feet. It can be transmitted by clothing. The micro-organism causing it has not been discovered. With the clearance of the rookeries of our great towns, it is rapidly decreasing, and appears likely to become extinct. The _means of prevention_, in addition to the abatement of nuisances, including overcrowding, are isolation and disinfection (pages 319 and 325).

RELAPSING FEVER.

This disease was formerly common in this country, but except in some parts of Ireland has entirely died out. It is caused by a micro-organism (_Spirillum Obermeieri_) which can be detected in the blood. Inoculation of this will produce the disease in man or in monkeys.

Epidemics of relapsing fever commonly follow in the track of typhus fever; overcrowding and filth being especially associated with typhus, and starvation with relapsing fever, hence its name of “famine fever.”

ENTERIC OR TYPHOID FEVER.

Enteric fever causes its highest death-rate in early adult life, though it is not peculiar to any age. Eberth in 1880 discovered the _Bacillus typhosus_ in the spleen and other organs of enteric fever patients. This is commonly known as Eberth’s bacillus, and is the cause of enteric fever. A few years later it was isolated and can now be grown on agar or gelatine in laboratories. It closely resembles other bacilli which are normal inhabitants of the human intestine; but can be distinguished by certain tests. It is a small rod, rounded at its ends, and from 2 to 4 µ long and three times as long as broad. In the living state it is freely motile, and possesses a number of minute cilia or flagella. Apart from other means of distinction between it and other bacilli, _Grüber’s serum reaction_ enables its identity to be ascertained. The bacillus suspected to be the _Bac.-typhosus_ is cultivated in broth in the bacteriological laboratory. A small quantity of blood is taken from the finger of a patient known to be suffering from enteric fever. The serum is separated from the blood corpuscles of this blood by a centrifugalising machine. A drop of the blood serum is diluted with 100 drops of broth culture of the suspected bacillus. If the latter is not the _Bac.-typhosus_, the individual bacilli when a drop of the mixture is examined under the microscope, will continue to move about freely; if it is the _Bac.-typhosus_, the bacilli will adhere together in “clumps” and become immobile. Conversely a valuable means of ascertaining whether a suspected case is really suffering from enteric fever is secured, as this blood added to 30 times the amount of a pure culture of the _Bac.-typhosus_ in broth will cause the latter to “clump” within half-an-hour (_Widal reaction_). Higher dilutions are usually unnecessary.

The chief means of spread of enteric fever is by the urine and fæces; and nurses who have to empty bed-pans unless very careful to wash their hands afterwards, using the nail-brush, are very liable to become infected, probably when eating food afterwards. The urine in a considerable proportion of cases, contains the typhoid bacilli, and it is therefore most important that care should be exercised in the cleansing of all chamber utensils, and that the urine as well as the fæces should be rigidly disinfected (see page 331). The infectivity of enteric fever has been underrated in the past. When patients with this disease are nursed at home by relatives who do not appreciate the full importance of the necessary precautions, it is rather the rule than the exception for them to fall victims to its infection. Probably, sometimes the infection has been scattered as dust, owing to small particles of fæces or of urine having become dried on bed linen. The most absolute cleanliness is essential in nursing this disease. In hot climates there is reason to believe that infective dust may be blown about from privies.

_Insanitary local circumstances_ are an important means of spreading enteric fever. It is more prevalent where there are privies than where there are pail-closets; and more prevalent where there are pail-closets, than where water-closets are the rule. Defective drains or soil-pipes are frequently found in houses in which enteric fever originates, and there can be little doubt that the former are at least partially responsible for the latter. The exact link is doubtful. Probably infective dust is blown or aspirated into the room and is inhaled.

The most common cause of enteric fever is _infected food or water_. Of foods _milk_ not infrequently has been the means of spread of enteric fever. Large epidemics have been traced to this source. Usually this has arisen by washing the milk cans with or wilfully adding contaminated water to the milk. _Water_, whether added to milk or taken independently, must have contained the specific contagium (the _Bac.-typhosus_) of enteric fever, to enable it to cause enteric fever. Hence water from a contaminated stream is more likely to have produced this effect than well-water, unless a patient has had enteric fever in the house to which the well is attached, and his dejecta have contaminated the water. Surface waters or spring waters may be contaminated with sewage (as at Maidstone) or deep well waters through fissures (as at Worthing) and thus widespread epidemics be produced. After floods, rivers and wells are most likely to contain the specific contagium of enteric fever, as at such times surface impurities from middens, etc., are apt to be washed into the water. (See also pages 91 and 224).

The _means of prevention_ of enteric fever are the discovery and removal of the cause of an outbreak, and the isolation of each patient and disinfection of all discharges. An early means of diagnosis is secured by Widal’s reaction. This is especially useful in cases not presenting characteristic clinical symptoms. The recognition of a disease or at least the suspicion of its presence is an indispensable first step for the taking of precautionary measures.

CHOLERA.

Cholera, which was formerly so prevalent, now seldom occurs in this country, and at each successive visit to England its inroads have become less serious. At its last visit in 1893 it scarcely obtained a footing in the country. Thus in the epidemic of 1854 in England it caused 1080, in that of 1866 it caused 672, and in that of 1893 only 45 deaths per million of population. In this country at least it is chiefly spread by infected water and foods, especially by infected water; and the preceding figures form an excellent testimony to our improvement in this respect. For particulars of the Hamburg outbreak, see page 93. In its mode of prevalence and propagation it is very similar to enteric fever, being infectious by means of the evacuations. The means of prevention are the same as for enteric fever. Cholera was shown by Koch to be caused by what is known as the _comma bacillus_ or _spirillum_ of Asiatic cholera, so called because of its curved shape. It is from 1·5µ to 2·6µ long and ·5µ broad. For the supposed connection of enteric fever and cholera with movements of the ground-water, see page 225.

SUMMER OR EPIDEMIC DIARRHŒA

is a most fatal disease among infants in the third quarter of each year. It is chiefly a disease of urban life, and occurs to a preponderant extent among the children of the artisan and still more of the unskilled labouring classes. It is much less abundant in towns which have adopted the water-carriage system of sewage than in those retaining the conservancy methods of removal of excrement (page 198). Towns with the most perfect domestic and street scavenging arrangements have the least epidemic diarrhœa. An impervious soil favours a low diarrhœal mortality; while persons living on porous soils usually have much diarrhœa. I have shewn elsewhere that given two towns equally placed so far as social and sanitary conditions are concerned, their relative diarrhœal mortality is proportional to the height of the temperature and the deficiency of rainfall of each town, particularly the temperature and rainfall of the third quarter of each year. In other words there is a general inverse relationship between rainfall and diarrhœa and a direct relationship between temperature and diarrhœa. Thus wet and cool summers are adverse to diarrhœa. Ballard concluded that the summer rise of diarrhœal mortality does not commence until the mean temperature recorded by the 4-foot earth thermometer has attained somewhere about 56° F., no matter what may have been the temperature previously attained by the atmosphere. This is a convenient index, as the summer warmth does not immediately cause diarrhœa. All the above facts point to the conclusion that the fundamental condition favouring epidemic diarrhœa is an unclean soil, the particulate poison from which infects the air, and is swallowed most commonly with food, especially milk. Thus, diarrhœa, like enteric fever, is a “filth-disease.” As the contagium appears to gain entrance by food, the following card of precautions which is distributed each year in the poorer districts of Brighton may be reproduced here:

HOW TO PREVENT DIARRHŒA.

During the summer a large number of infants die from diarrhœa. Scarcely a single baby who was being suckled dies from this cause. It is evident, therefore, that in the prevention of this very fatal summer disease, precautions as to food are most important.

Attention to the following points would save many infants’ lives:—

1. _Do not wean your infant during the hot months_ of July, August and September. To begin artificial feeding during hot weather is very dangerous.

2. If feeding by hand is absolutely necessary, carefully follow these directions:

(_a_) _All milk should be boiled_ before being given to the infant.

(_b_) The infants’ food must be _prepared fresh each time_. (For particulars see below.) Milk and water, and still more “pap” or patent foods, if left two or three hours, “go bad,” and are then very highly dangerous to the infant.

(_c_) _All jugs_ or other utensils used _for storing milk must be scalded out_ and kept absolutely clean. They should be covered to prevent access of dust.

(_d_) _The feeding bottle must be thoroughly scalded after each meal_, and the tube thoroughly cleansed. It is best to use alternately two boat-shaped bottles without tubes. If the bottle smells sour, something is not clean, and the infant will suffer.

3. _Decomposing refuse_, such as decaying vegetables, bones, fish-heads, &c., _is a fertile source of Diarrhœa_. _It should be burnt_, and not placed in the dust-bin.

4. _Scrupulous cleanliness_ of the house, especially of the rooms where food is stored, is most important. Dust in every form is dangerous to health, and for removing it wet cleansing is preferable to dry. Thus washing and scrubbing are safer means of cleansing floors, &c., than sweeping.

5. _Report to the Sanitary Office_, Town Hall, any smells or choked closet or drain.

DIRECTIONS FOR PREPARATIONS OF INFANTS’ FOOD.

=For a Child aged= =Mix and then boil= =For each Meal= (1 part _fresh_ milk ) Under 6 weeks {2 parts water } 4 tablespoonsful. (1 teaspoonful cream )

=Mix and then boil= (1 part fresh milk ) 6 weeks old {1 part water } 8 tablespoonsful. (2 teaspoonsful cream)

=Mix and then boil= (2 parts fresh milk ) From 3 to six months old {1 part water } 8 tablespoonsful. (2 or 3 teaspoonsful ) cream.

The infant should _be fed at regular intervals only_, at first every two hours, the interval being gradually increased.

The infant should _be fed slowly_.

If the milk as prepared above disagrees, _freshly boiled barley water_ should be used instead of water.

The _addition of cream is necessary_ because cows’ milk is poorer in cream than mothers’ milk, and because it is very often made poorer still by mixing with separated milk before sale. _Deficiency of cream causes rickets._ A little sugar may also be added to the milk, but this must not be regarded as a substitute for the cream.

TETANUS.

Tetanus or lockjaw is not infectious, but is conveyed to man by the inoculation of a wound by dirt or earth which contains the tetanus bacillus. For this reason it is more apt to follow injuries to the hands or feet. Extreme cleanliness of wounds is the only practicable preventive means. Little is known of the history of the tetanus bacillus outside the body; and as to what soils contain it most abundantly. Wounds contaminated by horse manure appear to be especially dangerous.

GLANDERS.

Glanders is common in horses. It attacks the mucous membrane of the nose, causing ulceration. It is extremely infectious. =Farcy= is a more chronic form of the same disease, in which the so-called “farcy-buds” are produced. Its prevention can best be ensured by killing both actually diseased and suspected animals, if the latter give a reaction to mallein. _Mallein_ is a product allied to tuberculin, obtained from cultivations of the bacillus of glanders. It sets up febrile reaction in glandered, but not in healthy horses. Further preventive measures are the temporary closing of public drinking fountains for horses, and the thorough cleansing and disinfection of stables. Men, especially grooms, are sometimes infected by the horse, and the disease is commonly fatal.

HYDROPHOBIA.

Hydrophobia is the disease in man which is caused by the bite of a dog or other animal suffering from =rabies=. It is seldom if ever communicated otherwise than by inoculation. The _incubation period_ in the dog varies from three to six weeks, and in man is usually about the same; but occasionally it is much longer, occasionally even more than a year.

At the Pasteur Institute, Paris, patients who have been bitten by rabid dogs are treated by the inoculation of an attenuated virus of rabies derived from rabbits, with promising results.

Dogs only acquire rabies from dogs or other animals already rabid. So far as is known, it does not arise _de novo_. Hence the necessity for an extensive area of muzzling when cases of rabies occur. The enforcement of this plan has greatly reduced the amount of hydrophobia in this country in recent years. There has been much misplaced sympathy with dogs on this score. In the dog the symptoms of rabies occur in three stages: a _premonitory_ stage, in which the dog’s habits change, he becomes morose and quiet, and dribbles; a _second_ stage, in which he has paroxysms of fury, his voice is high-toned and croupy, and he cannot swallow water; and a third or paralytic stage, in which his jaws drop, he drags his hind legs and soon dies.

ERYSIPELAS.

Erysipelas occurs on various parts of the skin. It is caused by the inoculation through an abraded surface of a virulent form of the same streptococcus that commonly causes suppuration. It occurs chiefly in debilitated subjects. Some persons are specially prone to it, and may have many attacks. Erysipelas, like scarlet fever, occurs most in years in which there is deficient rainfall; and is probably conveyed by dust. It may spread, though exceptionally, from case to case.

YELLOW FEVER.

Yellow fever never occurs in England, except when imported from the West Indies or other countries in which it is endemic. It clings to seaport towns in hot countries; and as a permanent disease is only found when the mean winter temperature is at least 68°-72° F. A frost always stops an epidemic of this disease. The germs of this disease are communicated by mosquitoes, which act as an intermediate host. Dr. J. W. Lazear, although isolated from yellow fever cases, died of it seven days after submitting to the puncture of an infected mosquito, thus proving the communicability of this disease, and entitling himself to an honoured position among scientific martyrs.

PLAGUE.

Plague is an Eastern disease, which occasionally shows a tendency to become widely epidemic. It is due to a rod-shaped bacterium, averaging ·8 µ to 1·6 µ in length, which does not form spores. In its characteristic form patients suffering from this disease have inflammatary swellings (buboes) of various glands: hence the name _Bubonic Plague_. In other cases it simulates ordinary pneumonia, typhus or septicaemia; or the patient may be so slightly ill as to be able to walk about. It appears probable that the bacillus enters the body through cracks or other lesions of the skin, possibly also by inhaling infective dust. The rat is an important factor in the spread of plague. Very commonly plague has been widely prevalent and fatal among them before it attacks human beings. Rats also bring it in ships from infected ports. Hence one of the most important preventive measures is to kill all rats on board ship, before the cargo is unloaded. This has been done by sulphurous acid fumigation in the holds. The use of carbonic oxide gas will probably be found practicable for the same purpose. Manson has put the importance of this point tersely as follows: “To prevent cholera the tea-kettle, malaria the mosquito net, and plague the rat-trap.” Flies may carry the infection (page 281). It has been suggested that the fleas of rats carry the infection (page 281).

ANTHRAX.

Anthrax is a very fatal disease in cattle and sheep, occasionally in pigs. Butchers may inoculate themselves with it when dressing a diseased carcase; the tanners similarly when handling the hide; and woolsorters may inhale it when sorting wool derived from a diseased animal (page 107). To prevent the latter, suspected wool must be disinfected by steam, and special arrangements made for carrying off the dust produced during sorting.

PUERPERAL FEVER

occurs after childbirth. It is caused like erysipelas by the inoculation of septic material. This may be conveyed by dirty instruments (syringes, etc.), or by dirty hands. Hence the importance of extreme cleanliness of hands, finger-nails, and all articles used during and after childbirth.

RHEUMATIC FEVER

has been commonly attributed to a damp condition of the atmosphere and soil. I have elsewhere shown that this is a mistake, probably arising from the fact that these conditions produce what are called “rheumatic” pains, though they have no true relationship with acute rheumatism (rheumatic fever). I have shown that rheumatic fever occurs chiefly in very dry years, the excess of prevalence in such years being sufficient to justify the use of the term “epidemic.” There is strong reason to believe that rheumatic fever is an infective disease, derived, not from other patients suffering from the same disease, but from some outside micro-organism which is ordinarily saprophytic. It follows the rule that when the lesion produced by an infective disease is deepseated (in the joints in this instance), no infection can be communicated to other persons. Some families are much more prone to rheumatic fever than others.

INFLUENZA

is, like diphtheria, a somewhat mysterious infectious disease. Like the latter it almost disappeared for a series of years, and then again became epidemic in 1889. The previous epidemics of influenza in the 19th century had occurred in 1803, 1833, 1837-8, and 1847-8. The causes of this recurrence of influenza are unknown. It is spread from person to person by direct infection, the infection being conveyed by the mucous discharge from the nose, throat, and lungs. Pocket-handkerchiefs probably are largely responsible for conveying the infection as dust. The disease is particularly fatal to the old; and these should not expose themselves to possible sources of infection, as in public places of assembly, during an epidemic. Every patient attacked with the disease should remain indoors for at least ten days. This is in his own interest, as he thus minimises the risk of such dangerous complications as pneumonia; and it is his duty in the interest of the rest of the community. Many lives might have been saved, had not influenzal patients “struggled about” during the early stages of the disease.

MALARIA.

=Malaria=, or =Ague=, is a generic name given to a disease caused by the invasion of the body by the _plasmodium malariæ_, discovered by Laveran in 1880. It occurs in two chief types, remittent fever and intermittent fever. For many generations it has been regarded as due to a marshy condition of the soil, associated with decaying vegetable matter, and a moderately high temperature. It is now clear that these conditions are necessary, only because they are necessary for the life of the mosquito. The well-known danger of being out of doors at night in a malarious country is explained by the nocturnal habits of the mosquito. The higher salubrity of the upper stories of houses is explained by the fact that the mosquito does not rise high from the ground; and of high-lying localities by their greater dryness. The value of the mosquito net, of smoke, and of fire as protections from malaria are due to their keeping mosquitos at a distance. The mosquito clings to the puddle or swamp where she was born, and where she will deposit her eggs. Hence the special danger of the immediate vicinity of such collections of water. Thus the prevention of malaria resolves itself chiefly into means for preventing the development of certain species of Anopheles (page 282). The conditions necessary for the multiplication of these are (1), an atmospheric temperature from 75° to 104° F.; (2) collections of fresh or slightly brackish water; and (3) the presence in these of low forms of animal and vegetable life. We have already described the cycle of life of the _plasmodium malariæ_ (page 282). Man is the chief, if not the only source, from which the mosquito derives this parasite. In native communities the young children, even when apparently not ill with malaria, nearly always harbour these parasites in their blood corpuscles. Hence the importance of Europeans having their dwellings as remote as possible from native houses. Mosquitos do not travel far.

Instances of the prevalence of malaria in the absence of mosquitos are not substantiated. The outbreaks of malaria where the soil has been disturbed after long lying uncultivated, probably mean the formation of puddles favourable to the breeding of the larvæ of mosquitos.

The necessary preventive measures are classified by Manson as:

1. Suppression of mosquitos. 2. Prevention of infection of mosquitos. 3. Prevention of infection by mosquitos.

The =suppression of mosquitos= involves the draining or filling in of swamps and ponds, the cleansing and canalisation of sluggish streams, and the afforestation of hills to prevent floods. Cultivation of rice and other plants entailing the prolonged flooding of land should be restricted to fields remote from dwellings. Subsoil drainage is helpful. The “painting” of stagnant waters with petroleum, which should be renewed every week or two, frees water for a considerable time from the larvæ of mosquitos. Eucalyptus and other balsamic trees may help to dry up pools, &c.

The =prevention of infection of mosquitos= is secured by insisting on all malarial patients using mosquito nets. This prevents the access of mosquitos. At the same time patients should vigorously and persistently take quinine, which kills the malarial parasites in the blood, and thus diminishes and finally removes the danger to other persons produced by the intermediation of the mosquito.

The =prevention of mosquito bites= is secured by rendering the house mosquito-proof by filling in all openings by fine wire gauze, and by having mosquito curtains to all beds; also by fumigating the rooms occasionally with the dried flowers of the chrysanthemum, by strict cleanliness of rooms, and by flushing them with sunlight. The proof of the mosquito theory as to the causation of malaria has been recently supplied by two test experiments. (_a_) In the first, a number of mosquitos which had been fed on the blood of malarious patients were sent to London from Rome. These were allowed to bite Dr. Manson’s son, who had never previously had malaria. A few days later he had a characteristic attack of fever. Malarial parasites were found in his blood. He recovered in a week’s time after free dosage with quinine, and the parasites disappeared from his blood. He suffered from a slight relapse about a year later. (_b_) On a fever-haunted spot in the Roman Campagna a wooden hut was built, and Drs. Sambon and Low, and three others took up their abode here during the malarious season, the only precautions taken being the use of mosquito nets and wire screens in doors and windows. They went about the country daily, but were always home before sunset. They all remained at the end of the season free from malaria.