Popular Science Monthly/Volume 26/March 1885/Cholera II
By Dr. MAX von PETTENKOFER.
II. MODES OF PROPAGATION.
HAVING now discussed the relations in time and space which predispose to cholera, I shall pass on to consider those relations in regard to the freedom from cholera which they may enjoin. Places which enjoy an immunity from cholera are more numerous than was formerly supposed, but have been less studied from a point of view of epidemiology, just as relations in time have been but little investigated. The eye of the investigator has only fixed itself on the places where, and at the time when, cholera has reigned. We ought likewise to investigate the matter when and where cholera does not exist. Ordinarily a physician only bestirs himself when he is called to see a case. It has, however, not been so with me. Impressed with these notions, I went in 1868 to the place in Southern France which had enjoyed the greatest and most renowned immunity from cholera. Through the kindness of M. Fauvel, I was introduced to M. Luuyt, of Lyons. Although Lyons was in frequent communication with Marseilles and Paris when epidemics of cholera raged, yet the disease never showed itself in an epidemic form at Lyons. In 1849, for instance, Lyons was besieged, conquered, and invested by troops suffering from cholera. Then the town escaped, while the soldiers suffered severely. This immunity was certainly not due to greater cleanliness of that quarter of the town known as Croix Rousse; nor was it due to the social misery or to the wants of the working-classes; neither had the drainage or water-supply, which prior to 1858 was as bad as it could be, anything to do in the matter. So that the immunity was probably the result of natural conditions. The Lyonese had often congratulated themselves on this excellent gift of nature, but it is probable that the constant movement of air which the combined flow of two great rivers (the Rhône and the Saône) originate is the cause of the immunity, although the mistral (Mistralstürme) which scours Languedoc and Marseilles had never been able to drive the cholera away. The situation of Lyons is far different: the bed of the two rivers is composed of compact granite, which on the right bank of the Rhône and on both banks of the Saône rises high, being in places coated with lias, molasse, and thick mud strata. On the heights lie the parts of the town called Croix Rousse, Fourvière, and St. Juste; other quarters lie low—Perroche on a tonarue of land between the two rivers, Lvon Vaise on the right bank of the Saône, and Brotteaux and Guillotière on the alluvial soil of the left bank of the Rhône. The lower parts of Lyons are frequently and deeply flooded over, and yet the cholera never comes!
Just as the disposition to cholera in time and place may be due to two causes, so may the immunity from cholera be dependent either on the physical nature of the soil, as is the case in parts of Traunstein and Kienberg, or on the condition of the soil as regards moisture, as happened in the low-lying parts of Munich during the summer epidemic of 1873, or at Augsburg during the summer and winter of 1873, or at Munich in 1866. Such a degree of wetness as prevailed on those occasions may be a constant condition in some places; to this latter group the low-lying districts of Lyons belong. Indeed, both factors are at work in Lyons. In the high-lying parts the granite comes to the surface in many parts, and so a very efficient and natural drainage is secured. These districts may always be said to be free from cholera. The soil of the low-lying parts, situated on the banks of the Rhone, Brotteaux, Guillotière, and Perroche, has always a certain degree of humidity, which cholera when imported has to encounter. This moisture of the soil of parts of Lyons is dependent not only on rain, but also on the river Rhône. The impermeable bottom of its bed is of solid granite, to which fact I could bear personal testimony. This stratum of granite stretches from the left bank of the Rhône far inward, so that Lyons is built upon it; all the springs lie below the level of the surface of the waters of the Rhône, and so rise and fall with the river. In Paris, in Munich, and in Berlin the conditions are otherwise. Here the level of the subsoil water is above the level of the waters of the Seine, Isar, and Spree, respectively; this relation is the most general, so that Lyons is exceptional. In Lyons it may be said that a part of the Rhône runs subterraneously, so that the soil receives water from the river; whereas in Paris, Munich, and Berlin the direction of the water is constantly from the soil to the river. When the water rises in the beds of the Seine, Isar, and Spree, there is no penetration of the water into the porous soil, but rather a damming and stagnation in the discharge of the subsoil water. The granite of the Rhône, chiefly composed of large blocks of quartz, contains also much fine sand, which is able to suck up water to a considerable height in its capillary spaces, possibly as high as the zone of evaporation. I investigated the hardness and moisture of this quartz by actual digging. This part of Lyons is only at times free from cholera, and would be susceptible of an epidemic were some of its water taken away. That Lyons may be fatally visited was shown in the year of cholera, 1854. As I was studying the conditions of cholera in Lyons, I found that in 1854 no less than 500 deaths occurred from the disease; while at other times the town escaped with a dozen deaths. It also transpired that nearly three fourths of the deaths happened in Guillotière, and I must say, therefore, that in the year 1854 at least a part of Lyons suffered from an epidemic of cholera. The Lyonese were not pleased with this assertion, because they had always boasted of their immunity from cholera; they replied: "What are 500 deaths out of a population of 400,000? It is absurd to call that an epidemic!" Of course, it would not be right to speak of an epidemic of all Lyons, but most assuredly there existed an epidemic in a part of it. The higher-lying districts had enjoyed their usual immunity in 1854. In the times of cholera which followed 1854 Lyons preserved its freedom. In what respect did 1854 differ from all other years? In nothing but in the fact of its greater dryness. I availed myself of the observations of the meteorological station, and found that in this year the amount of evaporation was greater than the rainfall. Observations on the subsoil water were not to be obtained, but there was the register of the condition of the Rhone dating as far back as 1826. From 1826 to 1854 there was no lower register so lasting as that of the last year. These facts were sufficient to lead me to understand how the lower-lying parts of Lyons could be brought into a condition susceptible of an epidemic of cholera by the partial or total removal of the influence of the Rhône.
That too much as well as too little water in the soil is unfavorable to cholera is vouched for by a large mass of facts. As I watched the cholera in Bavaria during 1854 I was surprised to find that the marshy districts, where, as a rule, the poorest dwelt, were exempt from epidemics. The great Donau bog, which lies between Neuburg and Ingolstadt, was surrounded by the epidemic, but the disease did not enter the villages on the fen. On the Freisinger moors an epidemic occurred at Halbergmoos. On going thither the affected houses were found to stand on a tongue of land composed of quartz, which tongue reached inward on the moor. Reinhard had proved the same thing for Saxony. The northern part of Saxony, which lies on the Spree, is a highly malarious district. For the eleventh time that cholera visited Saxony it shunned this region of fever. I will not say that cholera can not be epidemic on a fen, but I do believe that when such an occurrence takes place we ought to ask ourselves what relation it may have with the state of moisture of the soil. The theory on the soil and subsoil water requires that a knowledge should be obtained of what takes place in and over the soil on the outbreak and on the cessation of cholera. It requires, as Port has said, a continuous record of facts. That cholera should very seldom be met with in the neighborhood of and on mountains is also in harmony with the disposition of cholera in respect of time; so that, as the frequency of cholera in these regions diminishes, the rainfall increases; the weather and cholera are equally capricious. Towns among mountains which are refuges for fugitives from cholera are but seldom situated on a soil which in and of itself would exclude cholera. Salzburg and Innsbruck have, for example, never yet been visited by cholera. Further, in 1866, these towns escaped, although a considerable influx took place from the scat of war where cholera raged. Salzburg, but still more Innsbruck, stands on the alluvial soil of the Salzbach and the Inn, as Munich stands on the Isar; but the first-named towns have about fifty per cent more rainfall than Munich. I can only imagine that the necessary degree of dryness for the development of cholera would be attained but very rarely in Salzburg and Innsbrück, just as occurred partially at Lyons in 1854, and in June, 1859, at Bombay, where cholera prevailed during the monsoons, which, as a rule, drive the cholera away.
The disposition of cholera in regard to time is also evidenced in the fact that the disease is so different in one and the same place at different times, or at like times in one and the same place, if different parts of the place have different kinds of soil. For instance, in Munich the houses situated on the clay ridge of the suburb of Haidhausen are never affected, but this exemption is certainly not due to the supposed prevention which clay soil in and of itself exerts against the development of the germs of cholera, but because the behavior of rain on clay and rocky soil is very different if the rain be equally distributed over the two kinds of soil. When the rocky soil at Munich was ready for cholera, the clay soil was not.
I shall now leave the arguments for the localists, and pass on to consider the circumstances which are favorable to the views of the contagionists.
That an epidemic of cholera does not permanently last in one place, but after a longer or shorter time ceases, is explained by the contagionists as due to the saturation of the population, whereby each individual acquires a protective influence against cholera similar to that acquired after vaccination as against small-pox and other like instances. This hypothesis does not explain why an epidemic is sometimes rapid and sometimes slow in its course, why it is sometimes vast in its ravages and at other times slight in its effects, while the condition of mankind remains practically the same. With as much reason might the localists assert that the germs of cholera find at different times the local conditions to be favorable or unfavorable with the natural consequences of growth or death. Now, in districts where cholera is endemic, as in the soil of Lower Bengal, it is easy to suppose that at one time the conditions for the multiplication of the germs are present, while at another time the opposite state prevails. The dormant condition of the germs must, 'for a limited time, frequently exist in districts outside India, This supposition will not explain the occurrence in the low-lying parts of Munich of the severe winter epidemic of 1873-'74, after the summer epidemic in the higher parts of the town had ceased. It follows that we must suppose that the germs which give rise to an epidemic may arrive at a place and there exist for some time (in Munich for three months) without showing any manifestations; and that, indeed, the germs may die before the necessary local conditions for their growth and multiplication are present. So that one might seek in vain to trace the connection between cases of cholera coming from without and the first cases of illness occurring in a place, as happened in 1883 at Damietta in Egypt, and in 1884 at Toulon in France. The germs may have arrived six months before without finding the necessary material for their growth, and consequently may die out before giving any signs of their existence.
How long the germs of cholera may remain latent in a place we have no evidence to show. There are cases in which we might say that a whole year elapses, but instead of that I think it can be shown that in Europe the germs die out. Since cholera has lasted for many years in Russia, some epidemiologists have supposed that in Russia in the North, just as in Lower Bengal in the South, cholera is endemic. The history of cholera, however, in two islands of the Mediterranean, Malta and Gozo, supplies an example to the effect that the germs of cholera may die out in the space of a few years, and that the germs must be again imported before fresh cases of Asiatic cholera can appear. The Islands of Malta and Gozo lie near one another, and are by nature so similar that it might be imagined that a single homogeneous rock had been split into two parts, a greater and a smaller, which lie as near together as possible in the water without touching one another. It is thus that the two islands project from the sea. Each has the same kind of soil, enjoys the same winds, the same sunshine and rain, the same population of Arabic origin, with like manners, customs, and daily intercourse. Vegetables, fruit, and cattle for slaughter pass daily from Gozo to Malta. The two islands differ in that Gozo has no direct intercourse with the world at large, while Malta is famous for its natural harbor. Both islands have experienced epidemics of cholera, but Malta was always invaded some weeks before Gozo. Finally, both islands show themselves equally susceptible to cholera. In 1865 in Malta 12 per 1,000 of the population, and in Gozo 10 per 1,000, died of cholera. The first case of cholera occurred in 1837 on May 26th in Malta, and on July 5th in Gozo; in 1850 it was June 9th and August 28th respectively. In 1854 and 1856, during the Crimean War, cases of cholera appeared in Malta and Gozo, but not in an epidemic form; nevertheless, sporadic cases first showed themselves in Malta. In the epidemic of 1865 the first case occurred in Malta on June 28th, and in Gozo on July 21st. This interval of time between Malta and Gozo makes me suspicious of the current doctrine that cholera can occur in places two days after the arrival of the infecting cases; for it has not been proved that cases might have arrived still earlier. The instance of Malta and Gozo clearly proves that cholera may have no long duration, that it is not autochthonic, that it is not brought by the wind, but that for its passage intercourse is necessary.
The facts of the influence of locality the contagionists can not deny; indeed, they accept the facts, but explain them in another way. Attempts are made to show by the localists and contagionists, how the germs of cholera spread by means of human intercourse may act in harmony with the conditions of soil and subsoil water. This is unfortunately still the darkest chapter in the book, and will probably remain so; but it is not darker than the explanation of the nature of another infectious disease, which is equally dependent on conditions of soil and water—namely, malarial fever. We are firmly convinced of its telluric and climatic origin, and yet a study of Von Hirsch's "Handbook on Historio-Geographical Pathology" shows how little we know. Whether the infective material gets to man from the air, or water; or food, or the sting of a gnat, and so forth, we know not; and if we examine the tables showing the appearance of ague in the different months of the year in Leipsic, Vienna, etc., we come to see that the tables are not so very different from those drawn up by Brauser on cholera. In malarial fevers it is doubted whether infection is conveyed by the drinking-water, whereas contagionists believe that cholera is propagated through this source. The drinking-water theory played a great part in the causation of epidemics in the middle ages; it was believed that wicked men, either Jews or Christians, had poisoned the springs from which death was drunk. For good health, pure water is as necessary as pure air, good food, comfortable quarters, and so forth. I myself am an enthusiast in the matter of drinking-water, but not from fear of cholera or typhoid fever, but simply from a pure love for the good. For the water is not only a necessary article of food, but a real pleasure, which I prefer, and believe to be more healthful than good wine or good beer. When water fails, man may suffer not only from cholera, but from all possible diseases. In places where cholera prevails the water may always be indicted, for the water-supply is always a part of the locality, and the doctrine will frequently hold good, because the part may be mistaken for the whole. Where the influence of the water is held up to the exclusion of all other local factors error is liable to creep in. In England, where the drinking-water theory is fully believed in, two like influences, in which every other local factor was excluded, were observed in the cholera epidemic of 1854. In one case, in a street in London which was supplied by two water companies, the Lambeth with pure water, and the Vauxhall with impure water, it was found that the cholera was practically limited to the houses supplied by the Vauxhall Company. I was so much impressed by this fact that I endeavored to see whether the epidemic of 1854 in Munich could not be explained on a similar hypothesis. But my researches led me to a negative result. Without doubting the facts observed in London, I am of opinion that the impure water of the Vauxhall Company did not spread the germs of cholera, for the propagation of cholera was not effected by this means in Munich, but that the water increased either the personal predisposition to cholera, or perhaps the local predisposition, since the water would be employed in the houses, and about the soil. Later on, in 1866, Letheby doubted the accuracy of the drinking-water theory, and proved that there had been considerable confusion; so that a house which was registered on the Lambeth Company, really drew its water supply from the main of the Vauxhall Company, and vice versa. The cholera epidemic of 1866 was essentially limited to East London. The East London Water Company supplied this district with water filtered from the river Lea. Letheby brought forward a series of facts to prove that we might with equal justice accuse the East London Gas Company, since the first case of cholera broke out at the gas-factory. A second instance in London was that with which the name of Dr. Snow is associated. Golden Square, a part of London with very deficient drainage, was the scene of a severe epidemic of cholera in 1854. The epidemic concentrated itself in Broad Street. There must have been some reason for this, and the reason must be discovered. Where Golden Square and Broad Street stood was formerly a place of burial for individuals dead of the plague. This pest-blast of a former century could walk from its grave in a. d. 1854 like the ghost in "Hamlet." But a narrower inspection proved that the old pest-field and the new cholera-field were not exactly coextensive. Now, however, another fact was brought to light, which led to the substitution of the drinking water as the cause. In the middle of Broad Street there stood a pump of which the water was much esteemed on account of its freshness. At the end of August, while the cholera was raging, it was found out that many sufferers had drunk of the pump-water, but the fact was not sufficiently decisive, and so a pathological experiment was required. In Broad Street there was a percussion-cap factory belonging to Mr. Eley. The persons of this establishment suffered from cholera, and many of them died. Mr. Eley remained well, but he did not live at the factory, though he went there daily and returned home to Hampstead after business, and there lived with his mother and a niece. His mother, who formerly lived in Broad Street, had a great liking for the water of the pump-well, which was shown in the fact that her son daily took home the water for his mother and niece. In Hampstead there had been no case of cholera until the mother and daughter fell ill and died of cholera, without having any other communication with Broad Street than through the means mentioned. What more is wanted? Who can doubt any longer? An experiment on two human beings with a disease which animals are not susceptible to! A sad privilege. Never before had facts received a more frivolous interpretation. Suppose, for a moment, that Mr. Eley had gone to and from Hampstead to Broad Street without having taken the water to his mother and niece; and, further, that they had become ill of the cholera without having drunk the pump-water, would it have been imagined that the cholera had been carried by the son, who remained in good health? The contagionists would probably reply that Mr. Eley may have had the cholera in a mild form. The localists would say that a poison locally originated might be passed on by healthy people without giving signs of illness in them. In 1854, for example, a young lawyer went from Munich to Darmstadt, where his father resided. Up to that time the father had never lived out of Darmstadt, and Darmstadt was as free from cholera as Hampstead, and the distance from Munich was much greater than Hampstead from Broad Street. The lawyer was as well in health as Mr. Eley had been, but the lawyer's father fell ill and died of cholera. There was no other factor in the case than the return of the son from Munich. Darmstadt enjoyed an immunity from cholera as great as that of Lyons, Versailles, Stuttgart, and many other large cities. In 1854 a workman went home from the Exhibition of Munich to Darmstadt, where he fell ill and died of cholera without the disease being spread to any other house, and no means for disinfection or isolation had been adopted. In 1866 Prussian troops were quartered in Darmstadt, and brought the cholera with them. About thirty of the soldiers became ill with cholera, and many of them succumbed; again, none of the inhabitants of Darmstadt had the disease. It must be admitted that Mrs. Eley might have been infected through the intercommunication of her son, just as the lawyer's father had been, without the intervention of drinking-water. The argument in favor of the drinking-water theory rests on the fact that the cholera ceased when the supply of water was cut off; but no notice was taken of the great majority of cases in which the water-springs were not closed, and the supply of water not cut off, and yet the epidemics came to an end. Again, in Broad Street the pump-handle was not taken off till September 8th. Now, an examination of the facts will show that the cholera was already subsiding. In Broad Street, on August 31st, there were thirty-one cases of cholera; on September 1st, one hundred and thirty-one cases; on the 2d, one hundred and twenty-five; on the 3d, fifty-eight; on the 4th, fifty-two; on the 5th, twenty-six; on the 6th, twenty-eight; on the 7th, twenty-two; and on the 8th, fourteen. Just as occurs in India and elsewhere, a violent epidemic generally subsides rapidly.
The further one investigates the drinking-water theory the more and more improbable does it appear. Robert Koch, too, the famous bacteriologist, has hitherto failed to substantiate the drinking-water theory, and I feel convinced that the time is not far distant when he will own that he has gone in the wrong direction. Koch has succeeded in finding the comma bacillus in a water-tank in a region where cholera was prevalent. I have the greatest respect for this important discovery, not as a solution of the cholera question, but only as a very promising field for pathological, not epidemiological, inquiry. It must be remembered that cholera was already prevalent in the neighborhood of the water-tank from which Koch obtained the bacillus. Now, this tank was used not only for drinking purposes, but also for bathing the person and washing clothes, as Koch himself admits. According to my view the comma bacillus must have been present in the water. It had not been shown, however, that the bacillus was in the water before the outbreak of cholera. Koch is of opinion that all the bacilli in the water-tank could not have come from the washing of clothes of cholera-patients, but must have partly been derived from multiplication, yet he forgets that, as he himself has shown, the meat-broth in which the bacilli grow must not be too dilute. It would have been interesting if Koch had estimated the strength of the nutritive material in the water-tank. But what chiefly contradicts the doctrines of the contagionists is the simultaneous disappearance of the cholera on land and the cholera bacillus in the water-tank. If it were really true that every case of cholera, the first as well as the last in an epidemic, had the same infective material in its intestinal discharge, and that the epidemic only ceased because the susceptibility of man had passed away, then the bacillus would continue to exist in the tank, always supposing that there was sufficient pabulum for it. And thus it is most probable that the bacillus gets into the tank from man, and not vice versa. While Koch was in Calcutta the English physicians there imbued him with their views on cholera and drinking-water. The English had been brought up on the drinking-water theory of typhoid fever and cholera, and could only lay it aside with difficulty. But a few of those English physicians who had studied wide-spread epidemics had renounced their original ideas. Dr. Bryden (the chief of the Statistical-Department), Dr. J. M. Cuningham (the sanitary commissioner). Dr. John Macpherson (the Inspector-General of the Bengal Army), Dr. Lewis, and Dr. Douglas Cunningham were all disbelievers in the drinking-water theory. Koch was further strengthened in his views, in opposition to the few Englishmen just named, from the fact that after Fort William in Calcutta was supplied with pure water no more cases of cholera occurred there, although it had formerly been ravaged by the disease. The gentlemen in Calcutta had not, however, told Koch the whole truth. For it was a fact that cholera had begun to decrease in Fort William since 1863, and yet the fresh water-supply was introduced as late as March 25, 1873. Moreover, it was not true that the only improvement then effected was a change in the water supply, for many other changes were carried out, the fortress being made a model of cleanliness. Alterations in the drainage of the soil were effected in and around the foundations of the building, which before this was nothing more than a morass during the rainy season; so that, inasmuch as the nature of the soil, as well as the drinking-water, was changed, the case of Fort William affords an argument as much in favor of the localists as it does for the contagionists. I may here call to mind an episode which was much commented on at the time, and which is perhaps of the nature of an experiment. Macnamara writes, in his work on cholera: "In connection with this position I may narrate a case which happened in another part of the country, but for which the facts can be vouched. Some dejecta from a case of cholera found their way into a jug of drinking-water, and the mixture was exposed to the heat of the sun for the day. Early the next morning a small quantity of this water was drunk by nineteen individuals. Nothing was noticed, either in the appearance or taste of the water, by those who had partaken of it. All remained well during the first day. On the following morning one man was seized with cholera as he awoke; the others remained well till the second day had passed, when two more cases of cholera occurred, and the day after that two other cases were observed. The rest of the party remained well till sunset of the third day, when again two were seized with illness. These were the last cases, and the other fourteen persons continued to enjoy immunity from Diarrhœa, cholera, or any disturbance of health." This case is, etiologically, not worth much. Where was the original case from which the infection was supposed to have come? Was it not possible for the nineteen persons to be brought under the same circumstances as those under which the original case had become affected? Were the nineteen in a place which was as a rule free from cholera, and could they only be affected through the drinking-water? Several cases in India are known to me where guests at a banquet having drunk no water were yet the victims of cholera. For instance, at a baptismal feast which a sergeant gave, a gallon and a half (six litres and three quarters) of rum was supplied. Twelve persons, including the man and his wife, sat down to the banquet, and on the following evening the whole of the group, except the baby which still lives in Calcutta, were in their graves. At this feast there was no question of a mixture of anything with the stools of cholera.
When I ask myself how it is that men usually astute can place such implicit reliance on the drinking-water theory, which entails such ambiguity and contradiction, I can only think of two reasons. Partly, no doubt, there exists the belief that on general hygienic grounds no stone should be left unturned in order to procure a good supply of water where it had previously been bad, and thus the fear of death and the devil proves stronger than the love of truth and God. Again, the drinking-water doctrine appears to many to be the lesser evil as compared with the threatening local and periodical predisposition, which implies a more mysterious and less definable conception. They imagine that the (to them) uncomfortable facts of time and place may be explained on the drinking-water doctrine. The places where the cholera excreta can contaminate the drinking-water have a local disposition, and the times at which even cholera prevails, and excreta may contaminate springs and water-courses, have to do with periodical dispositions, and thus they escape from explaining the subtile influences of soil and ground-water. But any one who thoroughly investigates the local and periodical factors in epidemics of cholera must reject such an explanation. A study of the tables previously given from Brauser places great obstacles in the way of accepting these doctrines. The constant periodicity of cholera in Calcutta or Madras can not thus be cleared up. In the same way it is impossible to understand on this doctrine how it is that the hot, dry season, which must be destructive to the bacilli, is the period during which cholera is most prevalent, and how it is that in the hot and wet season, which is favorable to the growth of bacilli, cholera is at its lowest ebb. That cholera and typhoid fever are more flourishing when the ground-water is sinking than when it is rising has been explained by the drinking-water theorists on the view that when the ground-water is falling it becomes more concentrated, thicker, and therefore more dangerous. Now, the prolonged researches of Wagner, Aubry, and Port have proved the direct opposite. When the ground-water is low it is always purer than when high. Dr. Port has studied for a number of years the state of the water in the garrisons of Munich, with a view of watching its relations with the movement of typhoid fever, and he has found that when the water began to be impure then a falling off in the disease might be predicted. Why this should be do has received an experimental explanation from Dr. Franz Hoffmann. Great and numerous are the objections to the explanation of the local disposition to cholera by means of the drinking-water doctrine. Lyons was until the year 1858 supplied with water from superficial wells. The analyses of the waters from a number of the wells prior to the introduction of a better supply would astonish any one. The contagionists get out of their difficulties by merely asserting that though it is always the water which transmits cholera, yet there are a thousand ways in which this may be accomplished. But we have already shown that severe epidemics may occur without drinking-water being implicated, and consequently it is questionable whether, in those epidemics where the water may have been a factor, other causes did not play a more important part in the development of the malady. It is for the contagionists to prove why the infection by drinking-water can only be verified in certain cases. The most popular argument of the contagionists is the proposition that cholera spreads by human intercourse, a fact which I unhesitatingly accept. But the interpretation which the contagionists put upon the fact is nullified by the fact itself, as is shown by a closer study of all the influences of intercommunication, whether by land or sea.
In many regions there are main streets running in watered valleys in the direction of the stream, and yet other principal streets having a direction at right angles to that of the stream. In these streets, as is well known, at short intervals there exist sites which may be dotted on a special map where the frequency of cholera may be investigated, just as I had done for the epidemic of 1854 in Bavaria. It transpired that the sites of the epidemic preferred to spread in the length of those streets in the valleys which followed the course of the stream. When, however, one investigated the epidemic spots in streets which cross valleys between which hills or table-lands lie, it was found that the cholera attacks those sites which lie in a valley which crosses the streets, and the places which are situate on the heights between two valleys are spared. In the valleys, however, which are only crossed by one principal road, the epidemic spreads itself in places which lie in the valley upward and downward in the direction of the river, although the intercommunication may be very slight and the river not navigable. In Central India for a long time the great rivers were the principal means of communication, and the cholera spread by preference along these routes. When in recent times the Indian railways were started, it was thought that cholera would forsake the old routes and travel along the railway. But such was found by Cornish not to be the case. Of course, the same statement holds good in Europe. Saxony is perhaps as thickly peopled and as much overrun with railways as any state in Germany. Since 1836 cholera prevailed in Saxony on no less than eleven different years; but, as Reinhard and Günther have proved, its propagation was not in any way directed by the developing network of railways. Certain places in Saxony always were the centers for cholera, and so remained despite the railways. Freiberg, in Saxony, was never visited by cholera either before or after the railway was completed, while certain parts of the Mulde and Pleisse Thal were regularly visited. As often as an epidemic of cholera broke out in North or South Germany, cases were observed in Saxony; but for an epidemic to develop in Saxony always required time. Every year in Saxony which was marked by a heavy death-rate from cholera was preceded by a year during which the mortality was comparatively slight. Thus, in 1849 there were 488 deaths; in 1850, 1,5.51; in 1865, 358; and in 1866, as many as 6,731; again, only four cases in 1872, but 365 in 1873.
If the cholera can be brought by sufferers direct from India to Toulon, where the sea-passage lasts only three weeks, then if the di s-ease prevail in North Germany it must always spread to South and West Germany, and inversely, since we have nothing but cholera on the one hand and healthy people on the other. But whoever studies the history of cholera will find nothing but contradictions of this postulate of the contagionists. In 1854 Berlin took no cholera from Munich, and in 1866 Munich received no cholera from Berlin, notwithstanding extensive intercommunication during the Industrial Exhibition and despite the war.