604 
POPULAR SCIENCE REVIEW. 
visions_, their fancies conjuring up spirits, whose names they 
shrieked out. Some asserted that they felt as if immersed in 
a stream of blood, which obliged them to leap so high ; while 
others saw the heavens open, and the Saviour enthroned with 
the Virgin Mary. The accounts of the dancing mania col- 
lected by Hecker at first sight seem almost fabulous, but 
cease to be so when we recollect the practices of certain 
modern religious sects and the accounts of the so-called 
revivals in the middle of the nineteenth century. 
From the preceding summary, it is obvious that epidemic 
diseases vary greatly in their nature. 
1. First we have diseases, such as small-pox, scarlet fever, 
and measles, which at the present day can only be traced to 
contagion, and some of which probably took their origin in 
the lower animals. 
2. There are , diseases, such as typhus, relapsing fever, 
enteric fever, and probably also plague, yellow fever, and 
cholera, which are capable of propagation by contagion in 
varying degrees, but which may also originate from the neg- 
lect of sanitary laws, aided by certain meteorological conditions. 
3. A third class, including agues, remittent fevers, and 
diarrhoea, are not at all contagious, but arise from malarious 
exhalations. 
4. A fourth class, including influenza, dysentery, and, 
perhaps, the sweating* sickness, are also not contagious, and 
arise from certain atmospheric conditions. 
5. The dancing mania differed from all other epidemic dis- 
eases in being purely mental, and in depending on the mere 
sight of a disagreeable nervous malady. 
