INTRODUCTION. 9 



paratively recent times, attributed to the influence of gods, 

 demons or other supernatural agencies. The superstitions 

 and crude beliefs of the past gave rise to a mass of gro- 

 tesque theories and fanciful speculations. But with all this 

 we hear of certain beliefs and practices which plainly fore- 

 shadowed those of the present day. Latin writers nearly 

 two thousand years ago recorded a relation between insects 

 and malaria which has but lately been proved and explained. 

 The isolation of lepers by the ancient Hebrews shows that the 

 infectious character of the disease has long been recognized, 

 though other affections than leprosy were probably confused 

 with this disease by the ancients. "He is unclean: he shall 

 dwell alone; without the camp shall his habitation be" 

 (Lev. XIII. , 46). There is, in fact, much in the laws of 

 Moses that points to some knowledge of the nature of infec- 

 tions. "This is the law, when a man dieth in a tent: all that 

 come into the tent and all that is in the tent shall be unclean 

 for seven days. And every open vessel which has no covering 

 upon it shall be unclean" (Numb. XIX., 14, 15). 



"Everything that may abide the fire, ye shall make it go 

 through the fire, and it shall be clean" (Numb. XXXL, 23). 



In Homer we read of Ulysses, that, having slain his wife's 

 troublesome suitors: 



"With fire and sulphur, cure of noxious fumes, 

 He purged the walls and blood-polluted rooms" (Pope's Odyssey). 



The massive aqueducts of the Romans still remain to testify 

 that they understood the importance of a pure water-supply. 



In Rome there were also sewers for the disposal of drainage, 

 while the Cretans and Assyrians used sewerage systems hun- 

 dreds and even thousands of years before. 



About the fourteenth century we find quarantine against 

 infectious diseases, plague in particular, practiced by certain 

 Italian cities; and the word "quarantine" came into use from 



