EPIDEMICS^ PAST AND PRESENT. 603 
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siderable distance by tbe wind. A bigb temperature and 
rank vegetation seem to favour tbeir production and to in- 
crease tbeir virulence. 
13. Influenza . — Severe and wide-spread epidemics of influ- 
enza have been observed in various parts of the world from 
time immemorial. In the present century the disease has 
been epidemic in this country in 1803_, 1831_, 1833, 1837, and 
1847. On each occasion, it has been particularly fatal in aged 
and debilitated persons, and it has often been followed by 
an increased prevalence of other epidemic diseases. Influenza 
is not contagious, but depends on some unknown condition of 
the atmosphere. Sudden alternations of temperature have 
been thought to favour its origin. 
14. The Siueating Sickness . — This remarkable and very fatal 
disease is happily now unknown in this country ; but in the 
Middle Ages many great epidemics of it were observed, and 
nowhere were they more common than in England. Many 
of the epidemics were in fact conflned to England. There 
are records of five distinct visitations of the disease during 
the fifteenth and sixteenth centuries; viz., in 1485, 1506, 1517, 
1529, and 1551. The disease attacked all classes alike, and 
was often fatal within a few hours. From the accounts 
handed down to us, it is impossible to form any accurate idea 
as to the causes of its origin and extension ; but the prevalent 
opinion at the time seems to have been that it was due in 
the first instance to atmospheric influences. 
15. The Dancing Mania . — The present brief summary of 
the principal epidemic diseases would not be complete, without 
alluding to the dancing mania of the fourteenth and fifteenth 
centuries. The efiects of the Black Death of the fourteenth 
century had not yet subsided, and the graves of millions of its 
victims were scarcely closed, when, we are told by Hecker, a 
strange delusion arose in Germany, which took possession of 
the minds of men, and, in spite of the divinity of our nature, 
hurried away body and soul into the magic circle of hellish 
superstition. It was a convulsion which in the most extraor- 
dinary manner infuriated the human frame, and excited the 
astonishment of contemporaries for more than two centuries, 
since which time it has never reappeared. It was called the 
dance of St. John or of St. Yitus, on account of the Bacchantic 
leaps by which it was characterized, and which gave to those 
affected, whilst performing their wild dance, and screaming 
and foaming. with fury, all the appearance of persons possessed. 
It was propagated by the sight of the sufferers, like a demo- 
niacal epidemic, over the whole of Germany and the neigh- 
bouring countries. While dancing, the infected persons were 
insensible to external impressions, but were haunted by 
