Part 42

The manner in which the arrival of a sick person may cause the dissemination of the disease in a previously healthy community is even better shown by the following histories of local outbreaks:

"The water-supply pipes of the town of Over Darwen were leaky, and the soil through which they passed was soaked at one spot by the sewage of a particular house. No harm resulted till a young lady suffering from typhoid fever was brought to this house from a distant place. Within three weeks of her arrival the disease broke out and 1500 persons were attacked. At Nunney a number of houses received their water-supply from a foul brook contaminated by the leakage of a cesspool of one of the houses, but no fever showed itself till a man ill with typhoid came from a distance to this house. In about fourteen days an outbreak of fever took place in all the houses."

There are many other observations which seem to render it certain that the alvine dejections are a most important medium by which typhoid fever is communicated to others; and yet there is no evidence that they possess this power in a fresh condition. They have been repeatedly examined, and even handled, with impunity, and, as has already been stated, it {250} is rare for the disease to be imparted to the immediate attendants upon the sick, or in a well-ventilated hospital to the other patients in the same ward, provided that the discharges are disinfected and removed immediately after being passed, and the bed-linen and clothes of the patient changed whenever they are soiled. The feces must therefore undergo some changes before they become possessed of virulent properties. This appears to be shown conclusively by the following facts: (1) laundresses who wash the soiled clothes of typhoid fever patients not infrequently contract the disease; (2) the occupants of houses connected by ill-trapped drains with sewers into which the discharges of such patients have found their way often suffer severely from the disease; and (3) the use of water polluted by such discharges is, as has already been shown, almost certain to induce the disease in persons not protected by a previous attack.

The following histories of outbreaks of typhoid fever will show clearly how the dejections of patients may be the means of propagating the disease to others:

ILLUSTRATIVE CASES--Lausen is a village lying on the railway between Basle and Olten shortly before coming to the great Hauenstein Tunnel. It is situated in the Jura, in the valley of the Ergolz, and consists of 103 houses with 819 inhabitants. It was remarkably healthy, and resorted to on that account as a place of summer residence. With the exception of six houses it is supplied with water by a spring with two heads which rises above the village at the southern foot of a mountain called the Stockhalder, composed of oolite. The water is received into a well built covered reservoir, and is distributed by wooden pipes to four public fountains, whence it was drawn by the inhabitants. Six houses had an independent supply--five from wells, one from the mill-dam of a paper-factory. On August 7, 1872, ten inhabitants of Lausen, living in different houses, were seized by typhoid fever, and during the next nine days fifty-seven cases occurred, the only houses escaping being those six which were not supplied by the public fountains. The disease continued to spread, and in all 130 persons were attacked, and several children who had been sent to Lausen for the benefit of the fresh air fell ill after their return home. A careful investigation was made into the causes of this epidemic, and a complete explanation was given. Separated from the valley of the Ergolz, in which Lausen lies, by the Stockhalder, the mountain at the foot of which the spring supplying Lausen rises, is a side valley called the Furjust, traversed by a stream, the Furlenbach, which joins the Ergolz just below Lausen, the Stockhalder occupying the fork of the valley. The Furlenthal contains six farm-houses, which were supplied with drinking-water, not from the Furlenbach, but by a spring rising on the opposite side of the valley to the Stockhalder. Now, there was reason to believe that under certain circumstances water from the Furlenbach found its way under the Stockhalder into one of the heads of the fountain supplying Lausen. It was noticed that when the meadows on one side of the Furlenbach were irrigated, which was done periodically, the flow of water into the Lausen spring was increased, rendering it probable that the irrigation water percolated through the superficial strata and found its way under the Stockhalder by subterranean channels in the limestone rock. Moreover, some years before a {251} hole on one occasion formed close to the Furlenbach by the sinking in of the superficial strata, and the stream became diverted into it and disappeared, while shortly afterward the spring of Lausen began to flow much more abundantly. The hole was filled up, and the Furlenbach resumed its usual course. The Furlenbach was unquestionably contaminated by the privies of the adjacent farm-houses; the soil-pits communicated with it. Thus, from time immemorial, whenever the meadows of the Furlenthal were irrigated the contaminated water of the Furlenbach, after percolation through the superficial strata and a long underground course, helped to feed one of the two heads of the fountain supplying Lausen. The natural filtration, however, which it underwent rendered it perfectly bright and clear, and chemical examination showed it to be remarkably free from organic impurities, and Lausen was extremely healthy and free from fever. On June 10th one of the peasants of the Furlenthal fell ill with typhoid fever, the source of which was not clearly made out, and passed through a severe attack with relapses, so that he remained ill all summer; and on July 10th a girl in the same house, and in August a boy, were attacked. Their dejections were certainly, in part, thrown into the Furlenbach; and, moreover, the soil-pit of the privy communicated with the brook. In the middle of July the meadows of the Furlenthal were irrigated as usual for the hay crop, and within three weeks this was followed by the outbreak at Lausen.

In order to demonstrate the connection between the water-supply of Lausen and the Furlenbach, the following experiments were performed. The hole mentioned above as having on one occasion diverted the Furlenbach into the presumed subterranean channels under the Stockhalder was cleared out, and 18 cwt. of salt were dissolved in water and poured in, and the stream again diverted into it. The next day salt was found in the spring at Lausen. Fifty pounds of wheat flour were then poured into the hole, and the Furlenbach again diverted into it, but the spring at Lausen remained clear, and no reaction of starch could be obtained, showing that the water must have found its way under the Stockhalder, in part by percolation through the porous strata, and not by distinct channels.

Volz refers to an epidemic which occurred at Gerlachsheim, a village of Germany, some years ago, in which, in the course of three weeks, 52 persons residing on one of the principal streets were attacked by the disease. It was found, upon investigation, that they all got their water from a well which was polluted by the stools of the first patient. A. Pasteur reports an epidemic caused by the contamination of a well by typhoid dejections, and which ceased when the use of the water was discontinued. Niericker also reports an outbreak which was found to be due to a similar pollution of the drinking-water, and which likewise ceased when the water-supply was derived from another source.

An outbreak of the disease which occurred in a farm-house situated about eight miles from the city of Philadelphia came under my own observation. The first case occurred in a young girl of sixteen, who, with the exception of an occasional visit to the city, had not been away from her own home for several months before she was {252} taken ill. The disease ran in her a severe course, and eventually terminated fatally. About three weeks afterward four other members of the family were attacked, one of whom died. Two other persons, living in a house on the opposite side of the road, but who were in the habit of drinking water from the same well, also took the disease. There was no other case of typhoid fever in the immediate vicinity, nor had there been for some time. The farm-house is situated in a cup-shaped depression, so that water flowed toward it from all directions. The cellar was constantly filled with water during the winter, and just before the outbreak had contained not only an unusually large quantity, but also a large amount of decaying vegetable matter. The well from which the family drew their drinking-water is situated within a few feet of the kitchen door, and at some distance from the cesspool used by the family, so that there was no reason to believe that there was any communication between the two. The wall of the well was found to be very much loosened by the roots of two trees growing in the immediate vicinity. As the ground was also very much cut up by the burrows of rats, the water used for the various household purposes, and which was habitually thrown into a gutter which ran past the well, found a ready access to it. There would seem to be but little doubt that the first patient contracted the disease in some way during her visits to the city, and that the disease in the other patients arose from their drinking the water of the well which had been polluted by that used in washing her soiled linen.

Ballard has shown very clearly that milk may also be a medium of communication of the disease. He found that an epidemic which occurred in the parish of Islington, London, in 1871 was (1) almost entirely confined to a district comprised within a circle having a radius of not more than a quarter of a mile; (2) that out of 62 families living within this district, who were known to have suffered from typhoid fever, 54 were constantly supplied with milk from a particular dairy, and it was satisfactorily proved that at least three of the remaining eight had occasionally partaken from the same source; and (3) that out of 142 families, comprising all the customers of this dairy, and living not only within the district above specified, but in other parts of the parish, 70, or very nearly one-half, were invaded by typhoid fever within the ten weeks during which the outbreak lasted. Upon a visit to the farm from which the milk came it was ascertained that a member of the dairyman's family had been ill with typhoid fever, and that the water of the well which supplied the family with drinking-water had been polluted by his discharges. Although the dairyman denied that this water had ever been mixed with the milk, he admitted that it had been used to wash the milk-pans. Murchison was also able, in an outbreak which occurred in another district of London, to trace the disease to the same source.

Typhoid fever may be likewise propagated in consequence of the contamination of the atmosphere by the typhoid poison. This may be the result of allowing the undisinfected stools, or linen soiled by them, to remain for some time exposed to the air, or may arise from pollution {253} of the soil from the same cause or from defective sewage. Hermann Schmidt refers to several epidemics breaking out in garrisons which he believed to be due to pollution of the soil. In the citadel of Wurzburg typhoid fever occurred through several years, and persisted in spite of the cutting off of the water-supply, which was believed to be impure. It was finally found that the ground upon which it was built was saturated with all kinds of impurities. Volz refers to outbreaks of the disease from the same cause.

But perhaps the most striking example of this mode of propagation of the disease is that recorded by Budd, and is as follows: Two adjacent cottages, which for the sake of convenience may be designated as Nos. 1 and 2, had a privy in common, which was in the form of a lean-to against the gable end of No. 2. Through this privy there flowed with very feeble current a small stream which formed the natural drain for it. Having already performed this office for some twenty or thirty other houses higher up its course, the stream had acquired all the character of a common sewer before reaching the cottages in question. About a quarter of a mile farther on it acted as a drain for a privy, common as before, for two other cottages, Nos. 3 and 4. Notwithstanding the condition of the stream, which was so foul that it was said that the stink from it was often enough "to knock a man down," no evil result appeared to have occurred until a man living in No. 1 contracted typhoid fever--elsewhere, it was believed. As a matter of course, all his discharges were thrown into the common privy. In this way for more than a fortnight the stream which passed through it was daily fed with the specific excreta from the diseased intestines of the patient. No further cases occurred until the latter end of the third week or the beginning of the fourth week, when several persons were simultaneously attacked by the same fever in all four cottages. From first to last, the outbreak was confined to these four cottages, and there was no other case of typhoid fever at this time in the neighborhood.

The mattrass used by typhoid-fever patients, their bed-linen and clothes, have each been the medium by which the disease has been communicated to others. This is, as has already been pointed out, unquestionably due to the fact that these articles are generally soiled by their discharges, and that time has been allowed for the latter to acquire infective properties. It seems not improbable that the few cases in which the disease appears to have been contracted from the dead body may be explained in the same way. The statistics of the London Fever Hospital show that laundresses are more liable to contract typhoid fever than the immediate attendants upon the sick. This liability is greatest in those cases in which the bed-linen and clothes of patients are not immediately disinfected after use. According to Budd, the sputa in cases of typhoid fever where bronchitis is excessive may sometimes contain the germs of the disease, and mentioned a case in which he believed they were the means by which the disease was propagated.

The question naturally arises here, whether this is the only way in {254} which the disease can originate. This is a subject which has given rise to a good deal of controversy, and therefore demands some consideration at our hands. On the one hand, it is argued that typhoid fever never occurs in the absence of the specific poison or germ of the disease, and that this is contained principally, if not wholly, in the alvine dejections. On the other hand, it is contended that it may, and often does, originate spontaneously, and that all that is necessary to produce it is the presence of decomposing fecal or other organic matter, and the consequent contamination of the food, drink, or atmosphere. Both of these views have found able advocates. Among the upholders of the latter view is Murchison, who cites the histories of several outbreaks of typhoid fever which occurred in localities which had not been visited by it for many years, and which, after a careful investigation of all the circumstances attending them, he was forced to conclude had no connection with any previous case of the disease, and could only be explained by admitting that it might occasionally have an independent origin. Among the more remarkable of these outbreaks is the following, which we give in Murchison's own words:

"In August, 1829, 20 out of 22 boys at a school at Clapham within three hours were seized with fever, vomiting, purging, and excessive prostration. One other boy, aged three, had been attacked with similar symptoms two days before, and had died comatose in twenty-three hours; another boy, aged five, died in twenty-five hours; all the rest recovered. Suspicions were entertained that they had been poisoned, and a rigorous investigation ensued. The only cause which could be discovered was, that a drain at the back of the house, which had been choked up for many years, had been opened two days before the first case of illness, cleared out, and its contents spread over a garden adjoining the boys' playground. A most offensive effluvium escaped from the drain, and the boys had watched the workmen cleaning it out. This was considered to be the cause of the disease by Latham and Chambers, and by others who investigated the matter, and also by Sir Thomas Watson. The morbid appearances in the two fatal cases were described as like those of the common fevers of this country. Peyer's patches and the solitary glands of the small and large intestines were enlarged like 'condylomatous elevations,' and in one case the mucous membrane over them was slightly ulcerated. The mesenteric glands were enlarged and congested."

"A remarkable instance of a circumscribed outbreak of fever was recorded by Sir R. Christison in 1846. It occurred in an isolated farm-house in the thinly-peopled county of Peebles, N.B. Every one of the fifteen residents was seized with fever, and three died. Many of the servants who worked during the day at the farm were also affected, but none communicated the disease to their families who did not visit the farm. There was no evidence that the disease was imported from without, and the only explanation of the outbreak was, that the drains and sewers were found all closed and obstructed with the accumulated filth proceeding from the privies and farm-yard, the effluvia from which was very offensive."

"About Easter, 1848, a formidable outbreak of fever occurred in the Westminster School and the Abbey Cloisters, and for some days there {255} was a panic in the neighborhood respecting the 'Westminster fever.' No case of fever had occurred in the Abbey Cloisters for three years, and there was no evidence of its having been imported. Within little more than eleven days it affected thirty-six persons, all of the better class, and in three instances it proved fatal. Shortly before its first appearance there occurred two or three days of peculiarly hot weather, and a disagreeable stench, so powerful as to induce nausea, was complained of in the houses in question. It was found that the disease followed very exactly in its course the line of a foul and neglected private sewer or immense cesspool, in which fecal matter had been accumulating for years without any exit, and into which the contents of several small cesspools had been pumped immediately before the outbreak of fever. This elongated cesspool communicated by direct openings with the drains of all the houses in which it occurred; the only exception was that of several boys, who lived in a house at a little distance, but who were in the habit of playing every day in a yard in which there were several gully-holes opening into the foul drain."

The following cases would seem, however, to furnish stronger evidence in favor of the occasional spontaneous origin of typhoid fever than any of those referred to by Murchison. The first is recorded by P. Herbert Metcalfe, and occurred in Norfolk Island in the Pacific Ocean, 400 miles from the nearest inhabited land. The patient was a gentleman who had come from England four months previously. To Metcalfe's certain knowledge, there had been no typhoid fever on the island for fifteen months. Three years previously a man is reported to have died of it, and in 1868 there had been an epidemic of fever, but he could not ascertain of what kind. Upon inquiry, he found that his patient had been drinking water from a well which had the reputation of being unclean, and that he was the only person who had done so. He also found that at a distance of seven feet there was an open sewer, and that just opposite to the well much of the sewage-water became so stagnant as to form an offensive cesspool. The well was cleaned out, and at the bottom of it were found four feet of stinking sewage mud, the skeleton of a duck, a pig's jaw, etc. The well was so situated that had there been any typhoid fever previously to this case the water could not have been contaminated by the specific poison, as the above-named sewer only conveyed water from the kitchen, which is a building detached from the dwelling-houses of the mission, and is far from and on a higher level than the open closets in use.

In the second case, which is reported by R. Bruce Low, Medical Officer of Health, Helmsley, Yorkshire, occurred in a lad who had not been away from his home for months. No stranger had visited his house, and there was no fever in the district, the last case having occurred eight months previously in a sequestered valley eight miles away. The patient's habits and those of his family were revoltingly dirty. The garden privy was in bad repair, the filth level with the seat, and the smell from it very offensive. Thirty years before there had been five cases of slow typhus in the house. In his remarks on this case Low says: "This case did not owe its origin to direct infection, and the question naturally arises, was this a case originating de novo, or had the poison {256} been due to infection in some way or another from the cases which occurred thirty years previously?"

There can be but little doubt that in many of the cases cited by Murchison as instances of the spontaneous origin of typhoid fever there was an introduction of the germs of the disease from without. At all events, the evidence to the contrary is by no means convincing. For example, in the account of the outbreak at the Westminster School it is expressly stated that "the contents of several small cesspools had been pumped before the outbreak of the fever" into the large cesspool, the emanations from which it was believed had caused the fever. It does not seem that it was positively ascertained that none of these small cesspools had been used by a typhoid-fever patient, or that typhoid stools had not found their way into them in some other way. Moreover, in diseases generally admitted to be contagious it is not always possible to ascertain positively the source of infection in a particular instance. But after the elimination of all doubtful cases there yet remains a certain number in which it is reasonably certain that there has been no recent importation of the typhoid-fever germs, as in the case which is reported by Metcalfe and which occurred on Norfolk Island, and in that recorded by Low. The assumption does not seem an unwarranted one that in these cases the poison of the disease, which had been present before in a latent condition, had been suddenly called into activity by favoring influences. The following observation of Von Gietl shows the length of time typhoid-fever stools may retain their infective properties: "To a village free from typhoid an inhabitant returned suffering from the disease, which he had acquired at a distant place. His evacuations were buried in a dunghill. Some weeks later five persons, who were employed in removing dung from this heap, were attacked by typhoid fever; their alvine discharges were again buried deeply in the same heap, and nine months later one of two men who were employed in the complete removal of the dung was attacked and died." If we assume--and there is no reason to doubt that this point was fully investigated by Von Gietl--that the patient in the latter case had not been otherwise exposed to the causes of the disease, the observation shows that the stools in typhoid fever retain their virulence for nine months. If for nine months, why may they not do so for a much longer period--for as many years, for example? No probability is violated by this hypothesis. On the contrary, it is in full accordance with what we know of some of the lower forms of life, and will serve to explain many outbreaks of the disease which would otherwise be inexplicable--for example, the outbreak at Clapham referred to by Murchison. Admitting that the disease in this instance was really typhoid fever--and this has been denied by some observers, among whom is Sir Thomas Watson--the assumption does not seem an unwarrantable one that the germs of typhoid fever had been present in this choked-up drain long before it was cleared, but that in consequence of their exclusion from the air their infecting power was at a minimum. It was, on the contrary, much increased when the contents of the drain were exposed to the vivifying influence of the atmosphere.

On the other hand, it is alleged that an individual may be exposed to the direct emanations of sewers or of foul privies, or even drink water {257} contaminated by leakage from them, without contracting typhoid fever, so long as they do not contain the specific germ of the disease. Every physician in large practice, either in the city or country, can call to mind instances in which the air of houses or the water-supply has been polluted in this way, and yet no typhoid fever has occurred. Let, however, the specific cause of the disease be introduced from without, and this immunity almost invariably disappears. There is no reason to believe that the contamination of the water used by the family which suffered in the outbreak of the disease which has been already referred to as having come under my own observation last year was of recent origin. On the contrary, there was evidence to the contrary, and yet no disease occurred until it was imported by a member of the family who was in the habit of making frequent visits to the city. Even more strongly corroborative of this view is the history of the epidemic reported by Ballard, in which milk was the medium of communication. The water which had been used with impunity to wash the milk-pans, or perhaps to dilute the milk, became a source of danger only after the occurrence of the disease in the family of the dairyman.

Several epidemics of typhoid fever have been recently reported in which the disease appears to have been caused by the use of the flesh of diseased animals or of meat in a condition of putrefaction. In some of these the symptoms were rather those of irritant poisoning than of typhoid fever, and consisted principally in violent vomiting and purging coming on very shortly after the ingestion of the unwholesome food. There yet remains a certain number in which the symptoms cannot be thus explained. One of the most remarkable of these occurred in 1878 at a festival which was held at Kloten, a place about seven miles north of Zurich, of which the following is a condensed description: Out of 690 persons who sat down to the collation, 290 were taken ill; 378 other persons, who did not attend the festival, but who partook of the meat provided for it, were also affected. In addition these, 49 secondary cases occurred--i.e. of persons who subsequently became affected without having eaten of the meat. All other sources of infection could be certainly excluded, as Kloten was quite free from typhoid fever at the time, and as it was clearly shown that the water was not the cause of the outbreak. All the visitors at the festival who ate no meat escaped, as did also several persons who drank wine to excess and subsequently vomited. The period of incubation was short, as in other epidemics arising from the same cause. Some of the people were ill on the second day, with loss of appetite, nausea, headache, pain and swelling of the belly, and slight fever. These cases were slight, and generally ended in recovery. The greater number were affected between the fifth and ninth days. The symptoms in these cases, which usually ran a rapid course, and generally ended in recovery, were chills, fever, diarrhoea, great prostration, frequently violent delirium, and also profuse intestinal hemorrhage. The rose-colored eruption was present in almost all of them, and in a few the tâches bleuâtres were detected. On post-mortem {258} examination the characteristic appearances of typhoid fever were found. With regard to the meat supplied, the following facts were ascertained: Forty-two pounds of veal were furnished by a butcher at Seebach, taken from a calf which appears to have been at the point of death when it received the coup de grace from the hands of the butcher. All the flesh of the animal was sent to supply the festival at Kloten, but the liver was eaten by an inhabitant of Seebach, and he was attacked by typhoid fever. The brain was sent to the parsonage at Seebach, and all the household became affected by the same disease. It was also ascertained that another of the calves was diseased. The veal from this calf had been kept fourteen days, and was in a decomposed state. All the meat was placed together in the meat-receptacle of the inn at which the festival was held. This receptacle was in a horribly filthy state, and Cayley thinks there can be no doubt that the putrefying flesh of this last calf, together with the state of the receptacle, would rapidly excite decomposition in the whole supply.

Geissler, it is true, doubts whether the epidemic above described was really typhoid fever, and points out that the symptoms occurred too soon after the ingestion of the diseased meat, and reached their full development too rapidly. The cases were also accompanied by more pain in the abdomen than is generally met with in typhoid fever. The proportion of recoveries also appears to have been unusually large. Unquestionably, the patients in the Kloten epidemic were in a large number of instances simply suffering from the action of an irritant poison; but the presence of the characteristic lesions of typhoid fever in some of the fatal cases renders it certain that this disease also existed in the village at the same time.

In the report of this epidemic it is not stated that either of the calves which furnished a part of the meat for the entertainment were suffering from typhoid fever at the time they were slaughtered. It is now known positively that this animal is liable to be attacked by this disease, and a certain number of cases are on record in which the eating of the flesh of such animals has been followed by typhoid fever. That it does not oftener occur from this cause is probably due to the fact that a certain time must elapse before the flesh of such an animal acquires infective properties, and that it is usually used as food before this has been allowed to pass.

Ludwig Letzench asserts that he has produced some of the intestinal appearances of typhoid fever, as well as a high degree of pyrexia, in rabbits by the subcutaneous injection of the sputa and stools of typhoid fever patients.

THE BACILLUS TYPHOSUS.--From what has preceded, it will be seen that the writer is disposed to range himself with those who hold that the exciting cause of typhoid fever is an organized germ, or, in other words, a contagium vivum. Although this view cannot be regarded as positively proven as yet, it has recently received some support through the investigations of Klebs, Eberth of Zurich, and others, who believe that they {259} have found in the bodies of those who have died of typhoid fever a micro-organism peculiar to that disease.

Eberth (British Medical Journal, Nov. 26, 1881, from Virchow's Archiv, Bd. lxxxi. and lxxxiii.) has shown that in typhoid fever the intestinal mucous membrane, the mesenteric glands, and the spleen contain rod bacteria, differing, as he believes, from organisms found in the body in other conditions (among others in phthisis with extensive ulceration of the intestinal mucous membrane). In seventeen cases of typhoid these bacilli were found in six and wanting in eleven. In the six cases the number of bacilli were in inverse proportion to the duration of the disease. They were not found in the spleen in the cases of the longest duration, and only scantily in the mesenteric glands. These bacilli appear not to differ in shape and size from the ordinary rod bacteria, but Eberth believes that they differ from them in their small capacity for taking on the staining of hæmatoxylon, methyl-violet, and Bismarck brown.

Wernich's views (Vjhrschr. f. Off. Geshpfl., xiii. 4, p. 513, 1881) in regard to the nature of the Bacillus typhosus differ from those held by the two authors just quoted. He regards the specific Bacillus typhosus as nothing but the ordinary Bacillus subtilis of the large intestines, which under certain circumstances acquires the power to accommodate itself to the small intestines, to undergo a higher development and to become the exciting cause of disease.]

PERIOD OF INCUBATION.--The conditions under which typhoid fever occurs in large cities render it difficult, if not impossible, to arrive at a definite conclusion as to its period of incubation. Occasionally, however, the time which has intervened between the exposure to the cause and the invasion of the disease may be ascertained with precision in the outbreaks which occur in small towns or in isolated country-houses. Under these circumstances it has been found to vary within very wide limits. In the three cases related by Griesinger the attack began the day after exposure to the infection, and in the outbreak at the school at Clapham, referred to by Murchison, twenty out of twenty-two boys were seized with the disease within four days of exposure to the causes. Other instances of a similar character are on record. In cases like the above the rapidity with which the attack follows upon exposure to the cause is no doubt due to the intensity of the poison--a view which is to a certain extent at least supported by the fact that the invasion of the disease under these circumstances is very apt to be abrupt; the attack being often ushered in with vomiting and purging or with grave cerebral symptoms. Sometimes, indeed, the gastro-intestinal symptoms have been so violent as to have given rise to suspicions of criminal or accidental poisoning. In the majority of cases, however, the period of incubation is probably very much longer than in those above referred to. In the outbreak which recently occurred in a farm-house about seven miles distant from {260} Philadelphia, the history of which has already been given in detail, the second case began three weeks after the first, the other six following in rapid succession. In the celebrated epidemic which occurred at Lausen in Switzerland in 1872, and which is referred to by Cayley, the first ten patients were attacked within three weeks of the time when the contamination of the spring which supplied the village must have taken place, and these ten cases were followed in the course of nine days by fifty-seven others. In the town of Over Darwen 1500 persons were seized with typhoid fever within three weeks after a patient suffering from this disease was brought to a particular house, the sewage of which was allowed to soak into the ground through which the water-supply pipes of the town passed, and at a point at which they were leaky. Lothholz observed in an epidemic which occurred in the neighborhood of Jena that the average period of incubation was three weeks, the shortest period eighteen days, the longest twenty-eight days. Haegler found in three cases produced by contaminated water a period of at least three weeks. There are, however, epidemics on record in which the period of incubation was under two weeks, as, for instance, that of Basle, referred to by Liebermeister, in which a few persons were attacked who had only been in the city from seven to fourteen days. Cayley also refers to localized outbreaks of the disease, as those of Calne and Nunney, in which persons were attacked within fourteen days of their exposure to the cause. C. J. C. Muller of Posen says that the average period of incubation of the disease is fourteen days; that it may be not more than ten days, or, on the other hand, as long as from three to four weeks; and that he has known a case in which it was thirty-four days. Murchison believed that it was most commonly about two weeks, and William Budd arrived at the conclusion, from the observation of a large number of cases, that it varied from ten to fourteen days.