294 POPULAR SCIENCE MONTHLY. 



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 commis- 

 sioners 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 re- 

 searches 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 atmos- 

 phere 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 pre- 

 vailing epidemic disease. The last-mentioned disease is sometimes 

 known as " famine fever," on account of its liability to prevail in epi- 

 demic 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 en- 

 demic 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 dis- 

 ease 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 mor- 

 tality. 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 



