INTRODUCTION. 9 



the Hebrews resembles that now in vogue: "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 infections. 

 " 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. XXXI., 



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 fimd quarantine against 

 infectious diseases, plague in particular, practiced by certain 

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

 the fact that the period of detention was about forty days 

 (Ital. quarantina) .* 



Leeuwenhoek, a citizen of Delft, in Holland (1632-1723) 

 appears to have been the first who actually saw bacteria. Yeast- 

 cells he certainly observed, besides making many other con- 

 tributions of great value to biology. Leeuwenhoek produced 

 admirable lenses of high magnifying power, and described what 

 he witnessed with singular accuracy and enthusiasm. 



* T. M. Eager. The Early History of Quarantine. Yellow Fever Institute 

 Bulletin, No. 12. U. S. Marine Hospital Service. 



