1 8 Introduction. 



an infectious disease, but strongly partaking of an endemic 

 and hereditary character in its own proper focus, the borders 

 of the Nile, from North to South Egypt. Since 1177 it has 

 probably become less and less infectious, and more and 

 more hereditary. 



From a careful consideration of the three great epidemic 

 diseases plague, small-pox, and leprosy an epidemic 

 epoch or era has been assumed to recur about every 640 

 years from about 105 B.C. to 1817 A.D. 



It is supposed that whilst any given epoch runs over a 

 period not far short of 640 years, more or less, that it rather 

 gains in extension up to about 200 years. At this point it 

 remains moderately stationary for about 250 years, and then 

 begins to gradually decline. The faint outlines which history 

 supplies of the chronic disease leprosy, tend to confirm 

 this general view. The same may be said of small-pox and 

 plague, both of which are recorded in history a few 

 years subsequent to 537 A.D. ; but of this epidemic 

 era we hear but very little till a short time before the 

 next epidemic era of 1177. From this period the clouds of 

 pestilence drop their baneful dews and showers over all 

 Europe and Asia, increasing from century to century till 

 about 1660, when the devastation they threw broadcast upon 

 every city and country in Europe began to somewhat abate 

 and, in relation to plague, to almost die out. 



From 1348 to 1400 Black Death, as a graft upon Plague, 

 added greatly to mortality in Asia, Africa, and Europe. 



