Epidemics.— From the practical point of view there is no more interesting subject con nected with the public health than the rise, progress and decline of epidemics, the study of which now forms a special science known as epidemiology. From time immemorial civilized communities have been ravaged by plagues, pestilences and epidemics, which have at times enormously increased the death rate, as in the famous black death (see BLACK DEATH; PESTI LENCE; PLAGUE), and have thus made serious inroads upon the public health. With the dis-, appearance (until the Great War) of such dis eases as typhus (ship fever, jail fever) and of scurvy, both of which formerly destroyed thou sands even among civilized peoples, attention has of recent years been fixed more particularly upon the bubonic plague, which after a long absence from Europe has reappeared in great intensity in China and India, and has even threatened the shores of England and the United States. Asiatic cholera, which made a dramatic although brief appearance in the great commer cial city of Hamburg, Germany, in 1892 has since been kept at bay in civilized countries. Typhoid fever, however, still remains a curse of some even highly civilized communities, largely owing to the fact that it •is readily conveyed by food and drink, such as oysters, milk and water, while its specific germs appear to be more than usually hardy or resistant. But with the discovery of an effective serum or vaccine capable of conferring immunity against ty phoid fever, the dread of this disease is largely done way. Tuberculosis popularly called "the great white plague?' and which has always been credited with a very large proportion of the total mortality in all communities, still destroys perhaps larger numbers of people than any other one disease. Probably there was never a time (except perhaps in the middle of the 19th century in Great Britain) when a more general scientific, professional or popular interest has been felt in public health problems, and es pecially in the particular disease last mentioned, than to-day. As a result of the immense prog ress which has been made in our knowledge of the methods of dissemination of infectious and contagious diseases; and doubtless also in part because of the general improvements which the 19th century has witnessed in housing, heating and ventilation, and the better protection of the health of individuals as well as communities, a distinct decline in the death rate is apparent and a correspondingly greater longevity. It is im possible to determine how much influence should be credited to general improvements, the result of a higher degree of civilization, but after malting all deductions it probably still re mains true that life is safer and longer to-day than ever before, largely because of a better knowledge of the causes of disease and a better practice of the arts of hygiene and sanitation among the people. The discoveries which have been made in respect to the principal infectious and contagious diseases affecting the human race within the last 50 years have been so ex tensive and so cactraordinary that the names of these diseases have become almost household words, and the methods of dealing with them have become familiar, not only to physicians, but to sanitary experts, trained nurses and the intelligent public in general; and inasmuch as knowledge of this sort lies at the basis of ef fective promotion of the public health, we may briefly describe the more marked features of some of these diseases and especially the methods of their dissemination and control.
Before we do this, however, we may point out the remarkable fact that certain diseases which only two or three centuries ago rav aged the human race have been to-day almost completely exterminated from the higher civilizations. The most important of these is
probably the bubonic plaque, which in one form or another appeared in Europe down to the 19th century under the various names of the black death, the plague and pestilence. This dis ease is characterized (among other features) by swelling of the lymphatic glands, which turn black and suppurate, being then known as buboes, but it was not until the last decade of the 19th century that these buboes were found to be loaded with microbes (bacilli) capable of producing the disease in certain of the lower animals. Very late in the 19th century this plague, which had previously been for many years almost unknown in Europe and had never, so far as known, visited America, suddenly spread both westward and eastward from China. and menaced the coasts of Europe and America. It has, however, for the most part been success fully held in check, and is no longer greatly dreaded. Its method of dissemination is be lieved to be by means of rats and fleas, rats being very susceptible to the disease, and fleas which have bitten rats being abundantly capable of transferring the bacilli to human beings.
Another disease formerly very prevalent in highly civilized communities, which has within the last century or two practically disappeared, is typhus fever (spotted fever, jail fever, ship fever, etc.). This disease, which for a long time was not separated from typhoid fever in classifications, and which resembles it closely, but differs from it in the fact that it frequently causes extensive eruptions and is also lacking in the characteristic ulceration of the bowels which is the distinctive feature of typhoid fever, was formerly greatly dreaded, but, doubtless owing to the improved sanitation (greater clean liness) of crowded places such as jails and ships, has practically disappeared from among the most highly civilized peoples. Flow far better food and air have aided in the good work it is impossible to say. The main factor, how ever, is greater cleanliness, for it is now known that this disease is transmitted by lice, and that freedom from lice means, as a rule, free dom from typhus fever.
a disease formerly so prevalent that, according to one authority, 'scarce one in a thousand escaped it,'" and so much dreaded that the pesthouse in the early American towns and cities, a constant as well as a repulsive feature, was regarded almost with terror by many of the inhabitants, has of late years been nearly exterminated in the most highly civilized countries, and wherever sufficient pains have been taken to hold it in check by means of vac cination and revaccination. In the German army, for example, this disease is now ex tremely rare, apparently for the reason that vaccination and revaccination are most care fully attended to. The only serious danger from smallpox to-day is that communities which because of its scarcity are unfamiliar with the horrible character of the disease and its ravages may come to rely upon improved sanitation or other supposed safeguards and neglect vaccina tion which, according to 91I experience, is the only trustworthy defense against this extremely infectious and contagious disease. This danger is aggravated somewhat by the mistaken zeal of the so-called anti-vaccinationists, who, fixing their attention upon the occasional injuries con sequent upon vaccination rather than upon the enormous saving of life which has resulted from its use, maintain a propaganda against it, and seek to have vaccination entirely done away. However earnest and honest these persons may be, there can be no doubt in the minds of those who will take the trouble to review all of the evidence, that their contentions are largely un founded.