1 6 Introduction. 



for the assistance of infection by the men of that Crusade ; 

 and the seeds of infection, if that were required, arose from 

 the previous Crusades of a very insubordinate position, 

 from 1146 to 1187, to the famous one under Philip II., of 

 France, and Richard I., of England, in 1190. 



About the year 1600, or not far distant, leprosy ceased in 

 our own country, and scarcely held its own in Northern 

 Europe after that time ; but in Spain it was well known in 

 1764, and later. 



Hence, three well-known diseases, or four, as measles and 

 small-pox, which were twin-brothers, born and fostered in 

 Arabia, appeared as wide-spreading and infectious diseases 

 not far from the year 1177 in England, and Mid or Northern 

 Europe, at least north of the Apennines and Carpathian 

 ranges. 



These diseases each had for about 640 years, more or 

 less, a prior distinct existence in the lands north and south 

 of the Mediterranean, extending backwards from 1177 to 537. 

 In 572 small-pox was not only known in Arabia, but had 

 found its way into the literature of that country. Plague 

 had broken out in the reign of Justinian in 543, or earlier, 

 and again in 566, and had swept its thousands and tens of 

 thousands of human beings from off the face of the earth ; but 

 there appears to be no authentic record of this disease reach- 

 ing Mid or Northern Europe at these times; whilst leprosy 

 showed itself in Italy in 614, and as a well-known disease in 

 Spain in 714. How long, from its very chronic character, 



