602 
POPULAE SCIENCE EEVIEW. 
where it was impossible to believe that it was imported. It 
is a remarkable circumstance also_, that some of the greatest 
epidemics which have occurred in India, as that of 1861, have 
shown no tendency to travel to Europe, notwithstanding the 
constant communication that exists. Even on the supposi- 
tion, then, that cholera is of necessity imported from India, 
there must be something as yet unknown to us that favours 
its transmission at one time, and not at another. But it is 
very doubtful if the disease is imported in the manner gene- 
rally believed. Unequivocal cases of Asiatic cholera have 
been met with almost every year in the intervals of the great 
epidemics; and, as Ur. Farr has observed, it is highly pro- 
bable that true cholera has always existed in England. The 
researches of the late Dr. Snow render it highly probable 
that the disease often arises from drinking water impregnated 
with the fermenting excreta of persons suffering from the dis- 
ease ; and if this be so, from what we know of other diseases, 
it is not unreasonable to infer, that, in certain conditions of 
the atmosphere, the poison of cholera may be generated 
during the fermentation of the excreta of healthy persons. 
It can readily be conceived how the necessary meteorological 
conditions might originate in the East and gradually extend 
to this country, and thus lead to the supposition that the 
disease has been propagated by a specific poison. 
11. Dysentery . — Epidemics of dysentery are confined to 
tropical countries, and need not occupy much attention at pre- 
sent. Atmospheric states which unduly or suddenly depress 
the temperature of the surface of the body are the most com- 
mon exciting causes. They are most apt to take effect in the 
case of persons whose constitutions have been weakened by 
long exposure to extreme heat, to malaria, or to other dfebili- 
tating causes. There is no positive evidence that dysentery is 
contagious. 
12. Agues and Remittent Fevers are now but little known, 
and scarcely ever fatal, in this country. Many years ago, 
however, they were among the most common and the most 
fatal diseases of Britain. James I. and Oliver Cromwell both 
died of ague in London. The disappearance of ague has been 
in direct relation to the drainage and cultivation of the soil, 
and this remark applies not only to England, but to all parts 
of the globe. The fens of Lincolnshire and Cambridge are 
almost the only parts of England where agues are now 
known ; but in many countries, and particularly in the tropics 
where the vegetation is very rank, they are still the most 
common of all diseases. Agues are not contagious, but result 
from the malaria given off during the evaporation from marshy 
uncultivated land. These malaria may be wafted to a con- 
