6 THE POPULAR SCIENCE MONTHLY 



Nor is this all. There is another characteristic of this particular 

 group of diseases, which is quite as remarkable as those associated with 

 their inception and their cyclical course. They are catching, contagious, 

 infectious, communicable. They do not occur singly, but spread from 

 person to person, as flame leaps from tree to tree in a forest. The degree 

 to which this quality is manifest varies widely. When measles was first 

 carried to the unprotected inhabitants of the Faroe Islands, it spread 

 indeed, like wildfire, to almost every person. When smallpox is brought 

 into an unvaccinated community the same thing happens to-day. In 

 other communicable diseases, like tuberculosis and typhoid fever, the 

 transfer of infection is less inevitable and less direct. In all the maladies 

 of this type, however, the same principle obtains. The disease neither 

 originates within the patient nor comes, in the last analysis, from any 

 influence of earth or water or air. It arises ultimately in every instance 

 from a previous case of the same disease, from a specific spark of the 

 same conflagation. 



To the primitive mind, deeply tinged with anthropomorphism, the 

 natural explanation of all disease was sought in the evil influence of a 

 demon or other supernatural power. The plagues and pestilences in par- 

 ticular were punishments inflicted upon a people for their sins. There 

 was no possibility of escaping such visitations except by the dubious ex^ 

 pedient of flight ; no hope except in the relaxation of the celestial anger 

 of which they were the sign. As Defoe says of the cessation of the 

 plague in London : 



Nothing but the immediate finger of God, nothing but Omnipotent Power 

 could have done it. The contagion despised all medicine; death raged in every 

 corner; and had it gone on as it did then, a few weeks more would have cleared 

 the town of all and everything that had a soul. Men everywhere began to de- 

 spair; every heart failed them for fear; people were made desperate through the 

 anguish of their souls, and the terrors of death sat in the very faces and coun- 

 tenance of the people. 



The modern view that disease is not a divine infliction, but a natural 

 phenomenon, with natural causes, which may be progressively grasped 

 and controlled by the steady and disciplined activity of the human mind, 

 we owe first to the wonderful nation whose genius came to its flower on 

 the sea-girt promontories and islands of the iEgean twenty centuries ago. 

 Of all our debts to Greece there is none greater than this, that the 

 Greeks, first of all western nations, sought to find a natural rather than 

 a supernatural explanation of the phenomena in the world about them. 

 They often failed to find it, as was inevitable in the absence of the mass 

 of observations needed for good induction. They fell back on poetic 

 abstraction, almost as fanciful as the demons of their savage forefathers ; 

 in the case of the causation of disease, for example, upon the theory of 

 the four humors developed to a position of commanding influence by 

 Galen. Yet the great fact remained that whether the explanations of the 



