INCENTIVES TO THE STUDY. 13 



Plague in the circumstance that " a great multitude of people 

 from all quarters streamed into the city, and being cramped 

 for room, breathed corrupted air." Decomposing filth, social 

 squalor, bad weather, etc., were regarded as causes of disease, 

 by both physicians and laymen. 



INCENTIVES TO THE STUDY. 



When we turn our attention to the contagious diseases, to 

 the great plagues of past times, and watch the progress of 

 thought in regard to them, the absence of knowledge of the 

 means of staying their progress, the utter helplessness of the 

 people in times of pestilence, seems simply terrible. Without 

 a knowledge of the diseases of a country, we find it difficult 

 to understand aright its history or its civilization. These 

 great diseases have often destroyed the army of the conqueror, 

 or given the death blow to an advancing civilization, and 

 have left a strange and enduring impress upon the intellectual 

 life of great communities. It is generally known how, in the 

 Fourteenth Century, the most deadly of all the pestilences that 

 are recorded in past history the Black Death changed the 

 direction of intellectual and social activity throughout the 

 chief part of the civilized world, and showed its impress on 

 the developments of succeeding centuries. We can gain but 

 a faint idea to-day, through what we have seen around us, 

 of the devastation that may be caused by epidemic diseases 

 running without check ; or of the significance they have had 

 in the progress of civilization. 



The terrible results of epidemic and contagious diseases 

 have furnished the strongest possible incentives to the study 

 of the underlying causes. In all ages of the world the effort 

 to understand them has been unceasing. 



