# Popular Science Monthly/Volume 26/February 1885/Cholera I

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* CHOLERA.
By Dr. MAX VON PETTENKOFER.
I. ITS HOME AND ITS TRAVELS.
CHOLERA is an infectious disease. By infectious diseases are meant those diseases which are caused by the reception from without of specific infective material into healthy bodies, which material acts like a poison. To the list of infectious disorders belong such different maladies as small-pox and intermittent fever. Infective material differs essentially from lifeless chemical poison in being composed of the smallest possible units of living matter which when taken into healthy bodies rapidly increase and multiply under certain conditions and by their life-growth disturb the health of the body. These germs of disease belong to the smallest units of life, to the schizomycetes, which lie on the border-land of the invisible, and which, according to their form, are known as cocci, bacteria, bacilli, vibriones and spirilla, and thirty millions of which, according to Naëgeli, hardly weigh one milligramme! Infective material is derived partly from sick individuals, in which case the disease is termed "contagious" and partly from locality (earth), in which it has developed, in which case the resulting disease is termed "miasmatic." It is obvious that when derived from both sources the resulting affection was, and even now is, designated "contagio-miasmatic." I am of the opinion that the ​"contagium" and the "miasm," which have given rise to much misunderstanding, would best be dispensed with altogether; and that the designation "infective material" (Infectionstoff ), which is common to both contagium and miasm, should be divided into entogen and ectogen, according as the material is obtained from the sick body or the locality (soil). According to many, cholera would belong to the entogenous section, and according to others to the ectogenous division. The supporters of the first view might be termed "contagionists"; the supporters of the second "localists." As is always the case in medicine, the conflict of views is important, inasmuch as the measures to be adopted in the healing and prevention of a disease depend on the theoretical conception of it.
All readers know that cholera originated in the East Indies, and most individuals are also aware that the epidemic spread into Europe in the present century (1830), We shall first speak of its age in India, the home of cholera. There the disease appears to have existed at all times; not only at the time of the discovery of the sea-passage to India by the Portuguese, but long before, as the oldest Sanskrit writings show. Many hundreds of years before the birth of Christ the disease was accurately described and its epidemics spoken of as attended with mahá mâri (magna mors, great death). In these writings the disease appears under widely different names, which are taken from the chief symptoms: 1. Vishû dschikâ, vomiting and sweating; 2. Alasikâ, cramps which bring on exhaustion and stiffness; 3. Rilambikâ, which is perhaps best translated by the term "collapse." Another word which is often used in India is taken from the Mahratta, mordeshin or mordschi, which has been translated into French as mort de chien, but which also means "collapse."
In the seventeenth and eighteenth centuries a. d. there are abundant proofs and descriptions of epidemics of this disease. The disease is best known in Europe under the names of cholera, cholera morbus, Asiatic cholera, since the epidemic of 1817 to 1819, in which the English army, under the command of the Marquis of Hastings during a war against the natives, was rendered unfit for fighting and almost annihilated. But cholera had never visited Europe till the present century, when in 1830 it appeared in Russia and spread to Poland, where war was prevailing. Since that time, sometimes at longer and sometimes at shorter intervals, cholera has appeared in Europe. The question why cholera remained a thousand years in India before it first began to migrate is one of great interest, but one which can not be satisfactorily answered. The principal consideration appears to me to be that the event happened at the time when intercommunication in all directions, both by water and land, had become more rapid. The first steamship appeared in the Indian waters at the beginning of the second decade of the present century. By land also intercourse was greatly accelerated. The Russians possibly ​took cholera from India, Arabia, Afghanistan, or Persia, through couriers and stage-coaches. It soon became clear that cholera, the specific cholera-germ, was in some way or other propagated along the paths of human intercourse, and it also became evident that unless the germs found a suitable soil within a certain time they did not flourish. Observers soon discovered that cholera was more prone to appear in certain regions and to affect certain localities, while it shunned other districts; and, again, that other regions were only visited at intervals of many years. It is also a fact that Asiatic cholera never yet appeared at a place which had not previously been in communication with a region where cholera prevailed; and, further, that the disease from an infected locality never yet passed on to another place if the journey lasted a certain time without interruption. The large intercourse between India and Europe, more particularly England, by means of ships which sailed round the Cape of Good Hope, had never succeeded in carrying cholera from India to England; it was only by the overland route that cholera reached England. Neither had the Cape or Australia ever been visited by cholera. It is possible that in the future the communication may be so much accelerated that cholera may get to these countries. In much the same way South America escaped during the epidemic (1830-1840) in Europe and North America. It was supposed that in South America yellow fever was enough to prevent cholera, or that this disease kept out cholera, until suddenly, in 1854, after a service of fast sailing-vessels between Philadelphia and Rio de Janeiro had been established, the chief town in the Brazils experienced a terrible epidemic of cholera. When cholera passes overland it dies out unless it finds a suitable soil within a certain time. Rainless deserts are unfavorable to cholera. Caravans which pass from infected localities through deserts have never spread the disease, provided the journey in the desert lasted at least twenty days.
Cholera always requires for its propagation favorable stations on land, and, as a rule, if the course of epidemics be traced, a gradual extension in successive years is found to take place in fixed directions. In the east and southeast of Russia, for example, cholera prevailed after it bad raged in Persia in 1868; in 1869 eleven, and in 1870 thirty-seven provinces were affected, and among them five districts in Poland. In the year 1871 the epidemic spread into the west, east, and north of Russia, and succeeded in reaching East Prussia, when Königsberg was severely visited, so that from July 24th to November 8th, 2,012 individuals died there of cholera; while in Berlin only fifty-two and in Potsdam only seventy-one succumbed. In 1872 the epidemic reached Eastern Hungary, and in the following years reaped rich harvests in Germany. It has rightly been said, therefore, that cholera does not travel quicker than man. Nevertheless, the spring-like mode of progression of cholera is noteworthy: for example, it regularly jumps from Marseilles to Paris, or vice versa, passing over ​Lyons, the second largest town of France. Or, watching the passage over smaller distances, in 1854 it went from Munich to Augsburg by railway, leaving intact the ten intermediate stations, although several patients alighted and some even died; and, notwithstanding that cholera raged at Augsburg and Lech, it never once sprang over the valley of Lech to the town of Friedberg, which is but a league distant. Or, to take a still narrower circle, cholera thrice (1836, 1854, and 1873) invaded Munich, and every time halted in those houses situated on the clay soil in the suburbs.
The capriciousness of cholera may be observed in its relations not only to space but also to time; at one time it infected Prussia and shunned Saxony, while at another it did exactly the reverse. In the year 1849 Berlin experienced its worst epidemic, an epidemic in which Saxony was but slightly affected (488 cases) and Bavaria not more so. In the year 1850, when the cholera in Berlin and its environs had almost subsided, the epidemic raged in Saxony until 1,551 deaths occurred, though Bavaria was not involved. In 1854 the matter was altogether different; then Munich and Bavaria had its worst epidemic, at which time the Industrial Exhibition was held at Munich, and the intercourse between Munich and Saxony and the whole of Germany was very active. The cholera did not, however, spread to Saxony. All the fatal cases of cholera in Saxony had taken the disease from Munich. The epidemic did not spread farther north; yet the inhabitants of Saxony and Prussia had sufficient susceptibility for the disease, as was proved when they went to Munich. It was in the year 1855 that a change occurred; then Bavaria was exempt, and the epidemic devastated Saxony and North Germany, What relation the extension from India by the agency of man may have to conditions of time and space, to local and periodical disposition, has yet to be worked out; but the fact of the existence of relations in time and space is as undeniable as that of cholera itself. The cholera-germ alone will not explain everything. We must now inquire into the differences between places which are and those which are not susceptible, and endeavor also to trace out the relations in time which obtain in susceptible places.
No doubt can be entertained that the configuration of the earth has a certain influence. Relatively low-lying sites are very favorable to cholera. Where the surface of the earth has an undulating outline, it will be found that districts and individual houses which are situated on the summit of the undulation very frequently have no, or only a very small, disposition to the development of an epidemic of cholera, while in the hollow of the undulation under like conditions the opposite holds good. The truth of this statement is seen in single districts where parts or single houses exist on the summit and others lie low.
Another feature which is found in every epidemic is the falling off of the disease in the neighborhood of and on mountain-ranges. The Himalayan Mountains, those of Lebanon and the Alps, have always ​formed the places of refuge for fugitives from cholera. Now and then an epidemic occurs in the mountains; these exceptions will be dealt with later. The immunity, or the slight susceptibility, of mountain ranges for cholera is witnessed in India as plainly as it is in Europe. A familiar example is the complete freedom from cholera of the hill stations along the Himalayas, in which, through frequent changes of troops, the cholera has every chance of being taken up from the plains. In the severe epidemic of 1869 there were only two cases of cholera in nineteen hill-stations. A similar experience is met with in narrower areas. For instance, in Munich, 1873-'74, the frequency of cholera was widely different in the seven barracks of the garrison. In the low lying Isar Kaserne (occupied by cuirassiers, heavy cavalry regiment), out of one thousand men there were forty cases of cholera; in the highflying Max II Kaserne (with two field-artillery regiments) only three cases, and this without there being any difference in the construction of the caserns, the occupation or the diet of the men, or the drinking water. Another local factor, which is also very evident, is the nature of the soil. Where the soil is compact, and not, or very slightly, permeable for water and air, the development of cholera is much hindered. Some time ago Jameson, in his description of the epidemics of 1817 and 1819 in India, said, "Cholera does not appear to like a rocky soil." French epidemiologists (Boubée and others) have said the same thing. I studied this point in Bavaria in 1854, and then collected so many facts that I came to the conclusion that cholera requires for its epidemic development a porous soil through which air and water easily percolate, and that a compact soil was decidedly inimical. It will be sufficient to give a couple of illustrations. When the cholera broke out in Munich the inhabitants scattered themselves on the mountains. Many settled in the valleys, where several fell ill and died. The greater part of the town in which the better hotels were situated lies upon compact chalky soil, and the smaller part was built upon alluvial soil. In this part the cholera assumed an epidemic character. In the higher-lying districts (Schrödelgasse) the epidemic began in the beginning of August, and in the lower lying areas toward the end of September, while the greater part situated on chalk was not affected. Among the Jura Mountains to the left of the Donau lies a village called Kienberg, which is built on rock. In this village the cholera broke out so fiercely that within a month thirty per cent of the inhabitants died. When I went there I found many houses emptied, while other houses had not had a single case of illness. I then thought that the drinking-water was at fault. But the whole village drew water from a single spring at the foot of the slope on which the village was situated. From a study of the soil I found that all the houses built upon porous and rather loamy sand had been attacked, while those which lay upon the compact soil of the Jura rocks had escaped. The greater part of Kienberg stands upon a cleft of the ​mountain which had been filled up by fine soil which had resulted from the wearing down of the higher parts of the mountain (alluvial soil). That some doubt should be thrown on the decision of the commission which had adopted my views on the influence of the natural state of the soil on cholera was not to be wondered at. I spared no pains, however, in going to the Krain and Karst Mountains, where cholera apparently was raging on a bare, rocky soil, and instead of contradiction I found a further corroboration of my views. The towns lying among these mountains were found to suffer from an affection which unquestionably proceeds from the soil—namely, ague. The mountains are freely cleft, and the clefts are filled with porous soil, allowing of the free percolation of water and air, so as to be nothing more than an alluvial soil. Here streams rush down the mountain-side, turn off at its base, and run on richer still in water. You may often find there a cleft having the shape of a funnel, filled with porous earth; the nature of the cleft and its contained earth may be determined by sinking a so-called Dolione, when the bottom will be found to be solid stone. Through the Adelsberger growth the rapid Poik flows; and on the other side of the mountain in which the grotto is situated the waters of the Poik roll off under the name of the Unze; the Unze again flows off at the base of a mountain, as a navigable river, on the other side of Laybach. As I proceeded from Laybach to Novomsto (Neustadtl), I saw shining in the distance before me and far below the mountain a village, which turned out to be Rasderto, where I learned from my companion, a schoolmaster, that ague prevailed, and, indeed, I found many sufferers confined to bed from this complaint. Rasderto lies below the sites which the cholera infested. At the base of the rocky hills on which Rasderto is situated, there flows a stream which is so powerful that it turns a mill.
In order to study the cholera at Malta I proceeded thither in 1868 at my own expense. Mr. John Simon procured me the necessary introductions. On arriving in the harbor of Valetta I was forcibly struck with the rocky nature of the soil. The rocky hills rose high above the water, and on alighting on shore my feet encountered the resistance of bare rock. I ascended the steps hewed out of the solid rock, by which means I reached the plateau, on which the greater part of the town is built. A promenade, which was also shaped out of the natural rock, led me to my hotel. I now became very desirous for a further study of the place. Mr. Inglott, at that time the chief medical officer of the hospitals in Malta, and Dr. Pisani, a distinguished Maltese physician, rendered me very efficient aid in my researches. They often wondered why I had determined to visit Malta. How often did they say to me, when I questioned them on the nature of the soil of this rocky island, "Our rock is not rock in your sense of the term, but it is a sponge which sucks up everything which falls upon it" I Investigation proved that the Maltese rock was as porous ​as Berlin gravel, and that more than a third of its volume consisted of air-containing pores. It is so soft that it can be cut and sawed like wood. As visitors may purchase wood-carvings from Oberammergau and Berchtesffaden, so one can obtain carved-work of Maltese stone. Tiles cut from Maltese stone find a ready sale in Italy, where they serve to decorate the floors of rooms, where, owing to their porous nature, they are not so cold to the feet as stone tiles. Maltese tiles are as good as wood without being so inflammable. Moreover, of the same stone vessels are made which English sailors use to filter their drinking-water. Turbid water when poured into such vessels filters off as a transparent fluid. It will be readily understood that I now no longer concerned myself as to an explanation when I heard that an epidemic of cholera had broken out at a place which apparently had a compact soil.
Not only does the physical nature, but also the chemical constitution, of the soil have an influence on the occurrence of cholera—to wit, the presence of organic matter and water. The influence of the soil on the development of infectious diseases can only be understood by a study of the organic processes which take place in it. The processes are eventually dependent on the action of the lowest organisms, which require for their growth a certain temperature, so much water, air, and food-stuffs. In order to explain the occurrence of cholera on such varied soils as those composed of granite, sand-chalk, and shell-chalk, we must suppose that the soil contains in its interstices much organic matter and water. Farmers know how useless pure soil is, whereas the luxuriant growth of plants when the ground is manured is well known to all. These observations are applicable to the lowest plants, the bacteria, no less than to grain and vegetables. The germs of putrefaction and fermentation abound in the free atmosphere, but they only grow and multiply where they find suitable food. The hygienic uses of cleanliness here find their explanation and scientific foundation. The refuse from houses, dissolved or suspended in water, forms an excellent nutritive material for the lowest organisms which are so harmful to us. Emmerich has shown that the purest water after being used to clean the floor of a room contains in a very short space of time abundant germs of disease, so much so that a drop of it injected under the skin of a rabbit or Guinea-pig is followed by a fatal result. With this dangerous slop-water it is the custom to charge the earth in and about our dwellings. Since man began to live in towns where drainage was in vogue, diseases dependent on conditions of soil (cholera and typhoid fever) have undergone a striking decrease. Just as a field, when excessively manured, does not always remain good for vegetation unless remanured, so is it also with the uncleanliness of the soil in the neighborhood of our houses. As soon as we cease to make unclean—to manure—so soon do our towns begin to purify themselves, just as a churchyard after a time becomes purified. In a ​similar fashion does good drainage act in cleansing our towns, and the necessity of a pure water-supply is thus vindicated. It is in this way that, according to my view, cleanliness acts as a deterrent to cholera. Cholera-germs may come, but they can not fructify under such circumstances. That sites naturally exist which, without human interference, are unfavorable to cholera, has already been shown.
Where water entirely fails the organic processes soon come to an end; this is true of the soil of the earth. In rainless deserts the soil is dry except the most superficial layer during the night. In such desert places no organic processes can go on; this is shown not only in the absence of vegetation, but may be proved by an investigation of the nature of the air of the soil ("Grundlutt"); this air under ordinary circumstances contains much carbonic acid, which proceeds from the processes of organic life; but where the soil is free from water the air of the soil much more closely resembles that of the atmosphere above it. This fact has been experimentally proved by Professor von Zittel by a comparison of the free atmosphere with the air of the soil of the Libyan Desert. These observations are believed to explain how it is that cholera does not appear on a very dry soil. Just as too much water is bad for certain plants, so is it also for some members of the lowest class of the vegetable kingdom. It is likewise conceivable that the organic processes in the soil on which epidemics of cholera depend may be effectually checked by an excess of subsoil-water or by a want of material. Micro-organisms have been divided into two classes: anaerobe and aerobe. If now we have to deal with an organism which requires oxygen for its existence (aerobe), it is not difficult to understand how the excess of water might deprive the soil of the necessary proportion of air. The more the pores were filled with water the less air would be contained in the soil. In heavy clay soils the water drives the air completely out, and thorough desiccation would be required to replace all the air. Klebs and Tommasi-Crudeli have already discovered a micro-organism which flourishes only in a moist soil containing air—the bacillus malariæ.
We shall now inquire into the time relations of cholera at its permanent home in Lower Bengal. Dr. John Macpherson has, in his work on "Cholera in its Home," tabulated the number of cases of death from cholera in Calcutta for each month of the year for a period of twenty-six years. I have calculated and arranged in a tabular form from these statistics the average number of deaths in each month, and contrasted each month with the average rainfall at Calcutta. (See Table I.) It will be seen how unequally distributed is the great fall of rain, which is two or three times greater than in many districts of Germany. Calcutta has a rainy season, which begins at the end of May and ends at the beginning of October. The cholera decreases from the beginning and increases again toward the end of the rainy
Table I.
Average Frequency of Cholera, and Average Rainfall (in Inches') in Calcutta.
| —— | Jan. | Feb. | Mar. | April. | May. | June. | July. | Aug. | Sept. | Oct. | Nov. | Dec. | Total. |
| Cholera | 275 | 359 | 566 | 745 | 513 | 243 | 153 | 132 | 151 | 239 | 320 | 317 | 4013 |
| Rain | 0·21 | 0·42 | 1·43 | 2·40 | 4·29 | 10·1 | 13·9 | 14·4 | 10·4 | 4·2 | 0·9 | 0·13 | 62·58 |
(March and April), and its minimum is attained during the wettest and hot month of August, so that the curve of cholera falls while that of rain rises. The rise and fall of endemic cholera is constant, while the prevalence of cholera in its epidemic form is very variable. In the Punjaub the rain-winds (monsoons) bring with them the cholera. This apparent contradiction of the experience above mentioned may be explained by considering that the monsoons bring to the Punjaub the necessary moisture which is believed to be requisite for the development of an epidemic of cholera. Rain falls in the Punjaub at the same time as in Lower Bengal, but in smaller quantity. The average rainfall at Lahore is twenty-two inches, as compared with sixty-two inches at Calcutta; so that in Lahore for the greatest part of the year the soil is too dry for cholera. That these claims are substantial will be granted by a study of the rainfall and related circumstances in other parts of India. This is well seen at Madras, as indicated by Table II. At Madras the average rainfall is about forty-eight inches,
Table II.
Average Frequency of Cholera, and Average Rainfall (in Inches) in Madras.
| —— | Jan. | Feb. | Mar. | April. | May. | June. | July. | Aug. | Sept. | Oct. | Nov. | Dec. | Total. |
| Cholera | 194 | 191 | 123 | 64 | 65 | 59 | 164 | 191 | 186 | 143 | 93 | 104 | 1577 |
| Rain | 0·89 | 0·22 | 0·48 | 0·68 | 2·26 | 1·65 | 3·46 | 4·38 | 4·58 | 10·9 | 12·90 | 5·42 | 47·82 |
and is therefore midway between those of Lahore (twenty-two inches) and Calcutta (sixty-two inches), but the quantity of rain in the several months is different. The greatest quantity of rain falls in November, and Madras is not under the influence of the southwest, but of the northeast monsoon, and the rainy season extends from July to December. As Madras lies farther south than Calcutta, and the quantity of rain is twenty-five per cent less, it is plain that the desiccation during the dry and hot season would be much greater there than in Calcutta. And this state of affairs is reflected in the vegetation. April, May, and June are like winter months; the leaves begin to fall; the verdure fades away, and the sap descends to the roots of the trees, not because of the cold, but on account of the excessive dryness. It is at this period that cholera is at its minimum. In July, when the rain begins to fall, cholera increases, and reaches it maximum in August. The rain continues, but the cholera decreases, owing to the excessive dampness of the soil; so that in November a second minimum in the number of cases of cholera is met with. ​In order to inquire into the accuracy of these views, another observation, taken from India, may be cited. Places which are outside the region of endemic cholera, and which have a rainy season at the same time and of about the same amount as Calcutta, have the same amount and periodicity of cholera. Such an instance is afforded in Bombay, which is a city as large as Calcutta, and the rainy season of which depends on the southwest monsoons. In a table which shows the frequency of cholera, the rainfall, and the temperature on the average for a period of fifteen years, it is evident that in all three particulars there is a remarkable correspondence between Calcutta and Bombay. (See Table III.)
Table III.
Average Frequency of Cholera, Average Rainfall, and Average Temperature (in Degrees Centigrade), at Bombay.
| —— | Jan. | Feb. | Mar. | April. | May. | June. | July. | Aug. | Sept. | Oct. | Nov. | Dec. | Total. |
| Cholera | 235 | 213 | 263 | 295 | 294 | 278 | 162 | 93 | 60 | 76 | 95 | 163 | 2217 |
| Rain | 0·03 | 0·01 | 0·01 | 0·02 | 0·41 | 20·02 | 22·69 | 13·10 | 9·47 | 2·01 | 0·27 | 0·09 | 68·12 |
| Temperature | 24·1° | 27·7° | 26·2° | 29·1° | 30·4° | 29·1° | 25·2° | 25·2° | 27·1° | 27·2° | 26·2° | 24·7° | . . . . . |
The temperature has been given for the reason that it brings out the fact that temperature has not much influence on the progress of cholera. That Bombay is not within the endemic area of cholera is sufficiently testified by the results of the statistics for fifteen years. During this period there were three years in which no epidemic occurred. That a whole year should pass without the occurrence of a single case of cholera in Bombay is not to be expected, when the active intercourse between it and the endemic areas is borne in mind. If the table of averages relating to Bombay be compared with that of Calcutta, the resemblance is seen to be striking. The maximum incidence of cholera is seen to occur in both in April, and the minimum is found in Calcutta in August and in Bombay in September. After this minimum the increase takes place equally in both cities. The years during which no epidemic occurred in Bombay were characterized either by too much wet or too great dryness. Thus, in the years 1852-'53, the diminished frequency of cholera followed on a period of great wetness, and that of 1860-'61 came on after a very dry season. That this dependence on the weather is really sound is shown by a study of the years immediately following the lessened intensity of cholera. The years 1853-'54 and 186l-'62 in Bombay showed the same rhythm for cholera as Calcutta; whereas, on the contrary, the year 1858-'59 in Bombay had the same abnormal rhythm as Lahore. The average number of deaths from cholera in Bombay in March was 253, in April 295, and in May 291. In June, when the monsoons begin, the number further diminishes. The number of deaths in March, 1859, was 9, in April 7, in May 69, and, when in June the monsoons set in and 26·8 inches of rain fell, the number rose to 843, while the mean for June ​was only 278. After dry weather Bombay also shows, like Lahore, "monsoon cholera."
Cholera in India, as is well known, has likewise a remarkable relation in time to the years of drought in India. If rain once fail, or be very small in amount, a famine necessarily follows. Distress is then felt both in Lower Bengal and in the Punjaub, but the cholera only appears more severely in Lower Bengal and avoids altogether the Punjaub. The dependence of epidemics of cholera on the time of the year (i. e., on the moisture of the soil) comes out well in countries outside India, as, for example, in Germany. In the kingdom of Prussia from 1848 to 1860 cholera was prevalent every year, though its incidence varied in intensity and in different provinces. During this period cholera was as much at home in Prussia as in India. Brauser has collated the cases of death from cholera week by week for the thirteen years, 1848 to 1860. The numbers for the different months are as follows: April, 112; May, 446; June, 4,392; July, 8,480; August, 33,640; September, 56,561; October, 35,271; November, 17,530; December, 7,254; January, 2,317; February, 842; March, 214. The numbers are founded on statistics, and it is proper to investigate the possibility of errors therein. No objection can be made to the Prussian statistics, for the numbers are too great to be vitiated by casual error. In India the statistics may not be so trustworthy, because registration is sometimes defective. Some cases of death from cholera may not appear as such, and perhaps some deaths may be falsely registered as due to cholera. The Indian-statistics have, therefore, only been given for large cities, where more attention is paid to correct registration. The errors which may occur extend over all the months of the year, and are scattered, so there is less liability to perversion of the truth. And there is no need to prove absolute numbers, for relative statistics are sufficient. Further, in the garrisons and prisons of India, where physicians abound, the statistics are nearly as good as in Germany, since cholera is a disease so easily recognized. That a large series of numbers is able to eliminate to the vanishing-point the unavoidable errors of statistics is shown by an instructive example of the statistics of typhoid fever in Munich. Buhl, in studying the relations between the occurrence of typhoid fever and the state of the subsoil-water, made use only of figures obtained from the general hospital during the years 1856 to 1864, where every diagnosis was confirmed or overthrown by post-mortem examination. [Pettenkofer here devotes considerable space to the discussion of the question, dealing chiefly with the possible inconsistencies in the certificated causes of death, lie seems to prove that the difference between the numbers gained by actual observation and those obtained by calculation is so small that it may be disregarded.] It is considered that since the rate of death from typhoid fever in the general hospital is on the above showing a fair representative of the death-rate in the ​town of Munich, so the numbers concerning cholera obtained from the barracks and prisons of India may be taken as a good sample of the rate of mortality from cholera in the cities themselves. Bryden has given support, in his work on the time and space distribution of cholera in India, to the reports of barracks and prisons. That cholera should attain its greatest frequency in North Germany during the months of August, September, and October, and that winter should seldom see an epidemic, may be explained by the temperature which prevails in the air and earth. In the class of ectogenous infectious diseases, to which cholera belongs, the temperature, as in all organic processes, has a decided, though it can not be the chief, influence. That cholera is not very dependent on temperature is evidenced by the possibility of the occurrence of an epidemic of cholera during the winter. Why cholera spreads more during the summer and early autumn, as compared with winter and spring, must depend on other causes than temperature.
It is clear, in my opinion, that the soil and the moisture of the soil play a principal part. The dampness of the soil is, under certain conditions, clearly related to the subsoil-water, "Grundwasser." Epidemics of cholera abound during the time that the "Grundwasser" is falling, when the earth is comparatively dry. By "Grundwasser" is to be understood that condition of dampness of a porous soil when all the pores are filled with water. If water and air together fill up the interstices, then the soil is called simply damp. I have so long and so often spoken on the influence of the rise and fall of the ground-water on the frequency of typhoid fever and cholera, that I imagine a great many scientists credit me with the view that subsoil-water is highly harmful. But such is not the case. The subsoil-water is merely an indication of what is going on, and has no more to do with the actual processes than a dial and the hands have in the going of a clock. The fall of the ground-water by pumping away, or the rise of ground-water by the damming of a stream, has not the least effect on typhoid fever or cholera in the neighborhood. The observation of the level of the surface of the water in springs as an indication of the state of the subsoil-water is of no value from an etiological point of view, unless the spring be independent of the nearest water-course, and unless at the time of the observation the real state of the spring is a true reflex of the condition of the subsoil-water in its neighborhood. When the information, however, is obtained properly from springs free from objection, then the condition of the ground-water gives the state of moisture and of exchange in the overlying layers much more accurately than an observation made on the atmospheric downfall (rain and dew). Rain may fall for a week without causing any rise in the subsoil-water, and again a rise may occur when there has been no fall of rain for some time. The perusal of Professor Franz Hofmann's work, published in the "Archives of Hygiene," on the movement of subsoil-water, ​may be safely recommended. When an epidemic of cholera occurs in winter, then a relatively low state of the ground-water is found to prevail. In Munich three epidemics prevailed during the cold months: the first occurred between October and March, 1836-'37; the second from July to November, 1853-'54; and the third from July till April, 1873-'74. All three epidemics were associated with a relatively dry state of the earth, as was proved also by meteorological data concerning the rainfall. No investigation has been made as to the state of the ground-water during the period 1836 to 1854, but this investigation was first begun in 1856, so that for 1873 and 1874 the data were available; and it is only on the assumption that the condition of the soil as regards moisture was abnormal for the time of year that the long duration and strange division of the last epidemic could be accounted for. The subsoil-water sank from the end of June, 1873, till the beginning of August. On that occasion the germs of cholera probably came from Vienna, where the epidemic had prevailed since April. Two cases coming from Vienna, one in June, the other in July, could be vouched for. At the end of July the first illness from cholera occurred in Munich, but in individuals who had never come in direct contact with the infective cases. In every fresh outbreak, in 1836, in 1854, and in 1873, the same part (the northeast) of the town was the first to suffer. As the epidemics of 1854 and of 1873 developed at the same time of the year (the end of July), so by the middle of August the height of the epidemic was reached; it then fell off rapidly during September; during the whole of October only isolated cases occurred; and by the middle of November the epidemic had ceased in the higher lying parts of the town. It was thought that the disease had become extinct, and notwithstanding that it was considered strange that the summer epidemic had chiefly fallen upon the higher lying parts of the town, while the lower lying districts on this occasion had been altogether spared. In the middle of November, when the weather became colder, the epidemic reappeared, and attacked chiefly those lower lying districts which had escaped in the summer. It is impossible to trace the progress of contagion in time and space from one individual to another. The contagionists can not maintain that the unexpected falling off of cholera was due to the protection afforded by the previous prevalence of the disease, seeing that the lower lying districts had escaped the epidemic, and that the other inhabitants two months later suddenly lost their protection. Any one who studies the movements of the ground-water in Munich for the year in question will find that in the first half of August an event occurred which in suddenness and unexpectedness rivaled the retrogression of the epidemic in the second half of August. In the first half of this month there fell an abnormally large quantity of rain (one hundred and seventy-one millimetres), which excessive rainfall was the largest amount ever registered since the observations had been begun. The consequent wetness ​of the soil was reflected in a great abnormal rise in the ground-water. But from August onward through the winter, and till the beginning of the year, the amount of rain and dew which fell was again far below the average, and the ground-water steadily decreased. In the middle of April, 1874, it again began to rise, and then the epidemic of cholera ceased. The abnormal fall of rain in August, 1873, in Munich had the same effect on the cholera there as the southwest monsoons regularly have on the disease in Calcutta. In the relative dryness which follows this excessive wetness the epidemic process is continued as a winter invasion.
Munich and Augsburg are very much alike in situation and in meteorological factors. Both places lie in a direct line not sixty kilometres apart. But that differences in the amount of rainfall may occur is proved by the year of cholera 1873. In Munich, in spite of the excessive fall, the amount for the whole year was hardly up to the average; in Augsburg the excess above the average was thirty per cent. In 1873 the rainfall at Augsburg approached to that of the average at Salzburg. The distribution of the rainfall was different in Augsburg as contrasted with Munich, and the same difference in the history of the cholera holds good of the two towns. Augsburg had an epidemic of cholera in 1854, but none in 1836 or 1873, when only a few isolated cases occurred. That Augsburg in place and time and in individual disposition is susceptible of an epidemic of cholera was seen in the year 1854, when about three per cent of the whole population was destroyed by the malady, while Munich lost that year but two and a half per cent. If the appearance of cholera in the two places mentioned differed only in the time required for the transit from one city to another, then the germs of cholera must pass either from Munich to Augsburg or vice versa. In the year 1836 Augsburg remained free from cholera, which infested Munich for six months. At that period no observations on the rainfall were made, but no doubt exists that cases of cholera passed, without isolation or disinfection, from Munich to Augsburg. These facts prove that cholera is a miasmatic disease, and may be wholly independent of human intercourse. For the year 1854 meteorological data are obtainable, and this year had as dry a season in Augsburg as in Munich, while at both places cholera prevailed. In the year 1873 the case was different. Then there were in Augsburg regulations for the prevention of the spread of cholera, without which precautions, be it noted, in 1836, Augsburg remained free from the disease. Nevertheless, cholera did not visit Augsburg in 1873, during which period stringent measures of prevention were also in full force at Munich. Such considerations lead to the logical conclusion that what saved Augsburg did not relieve Munich. Further, Munich remained free from visitation in the humid summer of 1866, when cholera prevailed in North Germany; so that no importation of cholera to Munich took place from the seat of war.