284 Proceedings of Royal Society of Edinburgh. [sess. 
cholera to arise. Cholera may he introduced into a given area, 
and yet it does not necessarily follow that it will thrive in that 
area, and some definite local condition must exist for its propaga- 
tion. With regard to the influence of altitude, it may be said that, 
although cholera can penetrate to a considerable height, yet, unless 
in very severe epidemics, the number of cases are fewer the higher it 
ascends; and Farr adduced the law, that “ the proportion of deaths 
among the inhabitants from cholera is inversely as the elevation of 
the ground.” This law holds good, not only in high altitudes, hut 
in slight elevations in very limited areas. Ackland, writing on the 
mortality from cholera, mentioned the fact that in three epidemics 
of cholera in Oxford, in 1832, 1849, and 1854, the mortality 
per thousand people, living at a mean height of 30 feet above 
water-level, was respectively 3*3 and 1’8, as compared with 9 - 8 
and 5 ’3 deaths per thousand which occurred amongst the people 
living in the low-lying part of the town. There are, however, 
exceptions to this rule, as in some epidemics hilly districts have 
suffered more than the lower-lying surrounding country. 
Again, cholera follows the course of rivers, this probably being 
due to the fact that the riparian areas possess soil saturated with 
water and decaying organic matter. There can be no doubt, too, 
that cholera spreads most rapidly in countries having an alluvial or 
tertiary soil. 
With reference to the influence of weather on cholera, we know 
that the disease is met with under every known variety of climate ; 
yet doubtless a high temperature aids its spread, and most epidemics 
are brought to an end, or at least are most markedly reduced in 
extent, when the temperature falls greatly. The Yienna Confer- 
ence of 1884, in which were assembled representatives of all coun- 
tries, stated that there were no facts to show that atmospheric causes 
alone could bring on cholera, and also, that all facts go to show 
that in free air the generative principle of cholera rapidly loses 
its morbific character. 
With regard to the influence of the moisture of the atmosphere 
upon the production or spread of cholera, it would appear that a 
certain amount of moisture in the atmosphere, or perhaps more 
correctly speaking, in the soil, is needed for its development and 
spread; it is probable that spring showers or sudden summer 
