8 INTRODUCTION 



shall be unclean." (Numb. XIX, 14, 15). " Every thing 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). 



These records certainly suggest a rather advanced state of knowl- 

 edge concerning the nature of contagion. It may be that they 

 record customs derived from a superior knowledge of some other 

 ancient people, perhaps the ancient Egyptians. During the 

 middle ages, as doubtless also before the dawn of history, epi- 

 demic disease was regarded as a visitation of Providence or at- 

 tributed to the influence of gods, demons or other supernatural 

 agencies. Epidemics were associated with the appearance of 

 comets in the sky or with other evidences of divine wrath. These 

 conceptions of disease have not altogether disappeared even at 

 the present time. 



Hippocrates (400 B. C.) denied the supernatural causation 

 of disease and held that such doctrines were mere cloaks for help- 

 less ignorance. He ascribed epidemic disease to a morbid secre- 

 tion of the atmosphere, and later writers have expressed this 

 idea of a morbid secretion by the word miasm, its exact nature 

 remaining for centuries intangible and mysterious. There is 

 here a conception different from that upon which the hygienic 

 measures of the Persians and Hebrews were founded and the 

 distinction was clearly expressed by Pettenkofer in the nineteenth 

 century, who defined contagious diseases as those which are trans- 

 mitted directly from man to man or through the agency of solid 

 objects, while in miasmatic diseases the causative agent enters 

 from the outside world where it may live naturally or where it 

 must have undergone a ripening process since its escape from the 

 body of the sick person. As will be seen later these ideas apply 

 very well to certain diseases, for example, small-pox and syphilis 

 as contagious diseases and yellow-fever and malaria as a mias- 



