GREAT EPIDEMICS—ASIATIC CHOLERA. 283 
tionable and contradictory results. In Hurope, high re- 
gions have generally been spared, but the epidemic has 
raged violently on the plateaus of Mexico and the summits 
of the Himalayas. If localities overlying granite and other 
solid rocks have seemed to enjoy special immunity, as Pet- 
tenkofer has proved, cases are known, like that of Helsing- 
fors in 1849, in which those parts of the town built on 
granite were decimated, while the marshy parts and those 
near the shore remained exempt. Some countries, such as 
Wiirtemberg, some cities, Lyons for instance, have hitherto 
escaped the attacks of the pestilence almost wholly, with- 
out any assignable reason. What is more indisputable is 
the fact that the collection of multitudes of people facilitates 
the development of the disease. Armies in the field, popu- 
lous cities, make a sort of centre from which it radiates. 
Thus the war in Poland in 1831 seems to have been the cause 
of the rapid spread of the cholera in Europe. We know 
no instance of a rural population swept by the epidemic 
where there was not a town in the neighborhood which 
had first suffered from its effects. In the towns, the most 
closely-built and unwholesome quarters are attacked and 
affected more severely than the others. In a word, the chol- 
era has a special affinity for large collections of human be- 
ings; in them it concentrates, and through them it spreads. 
Observed facts are decisive in this respect, and no argument 
could prevail against the accumulated evidence. The close 
study of epidemics shows that we must attribute the more 
or less rapid spread of cholera beyond the centre of its ori- 
gin neither to winds nor to water-courses, nor to supposed 
miasmatic emanations, but it must be attributed to pilgrim- 
ages, fairs, movements of troops, and similar changes of 
place by masses of men. Single travelers in good health 
have, as may well be imagined, very few chances of carry- 
ing the disease with them from an infected country to a 
healthy one; but travelers in crowds, among whom there 
