demonstrated the fact that the bubonic plague is due to a bacillus. No doubt the present limited geographic range of this pestilential disease is due to the great sanitary improvements which have occurred in European countries during the past two centuries. The experiments of Yersin show that rats become infected and die when they are fed upon portions of the body of victims of the plague. He also demonstrated the presence of the plague bacilli in dead rats found in the houses and streets of Hong Kong. This may account for the perpetuation of the disease in a country where rats abound, and where the victims of the plague are no doubt frequently exposed to the attacks of these voracious animals. The epidemics of plague which have occurred in Europe, so far as we are able to trace them, appear to have had their origin in the Orient. The French commissioners who were sent to Egypt in 1828 to study plague arrived at a conclusion which is in consonance with our suggestion that rats may play an important part in perpetuating the malady. Their researches convinced them that plague was unknown in Egypt previous to the year 543 (a. d.), and that its first appearance corresponds with the time when the Egyptians discontinued the practice of embalming the dead, and resorted to burial in the earth, which among the poorer classes is commonly done in a manner so inadequate that the atmosphere around a graveyard is usually filled with the products of cadaveric decomposition.
The pestilential disease which prevailed so extensively in Europe during the middle ages, and which was known everywhere as the black death, caused an enormous loss of life. This disease is now believed by epidemiologists to be identical with the bubonic plague of the Orient. No doubt, however, other pestilential maladies, and especially typhus, or "spotted fever," were confounded with the prevailing epidemic disease. The last-mentioned disease is sometimes known as "famine fever," on account of its liability to prevail in epidemic form during periods of scarcity of food. Typhus was not recognized by physicians as a distinct disease until about the end of the fifteenth century, and typhoid fever, which prevails as an endemic disease in all parts of the civilized world, was not differentiated from typhus until the early part of the present century. There is, therefore, considerable confusion as regards the real nature of the disease in many of the epidemics which occurred in Europe during the middle ages, and even as late as the last century. But there can be no doubt that bubonic plague was one of the chief causes of mortality. It continued to prevail in various parts of Europe during the sixteenth century, and during two thirds of the seventeenth; but during the latter part of the seventeenth century it became more and more rare, and after the middle of the eighteenth century its only
