22 
the impurities which were deposited upon the leaves of plants 
during long periods of dry weather. The cattle plague is 
said to have had its origin in Central Asia, and in this region 
there is very little rain, and the daily range of temperature 
is very great. The herbage is therefore seldom well washed, 
and moreover, the cattle that feed upon it are exposed to 
frequent and violent changes of temperature. We have no 
report of any cattle plague breaking out among the herds 
on the pampas of South America, where rain falls more 
abundantly and the changes of temperature are much less 
violent. 
The President said that the idea of deriving the cattle 
plague or any similar epidemic from the organic matter 
brought down by dew was at least in harmony with much 
that we had learnt. The dews and fogs of evening over 
certain lands were known to produce colds, agues, or fevers 
which could be avoided by rising to a certain height from the 
ground. There seems little doubt that the moisture in such 
cases is not the cause of disease, but only the means of con- 
veyance. These diseases were produced by breathing the 
impure air. We know less of the effect when the matter is 
condensed and conveyed into the stomach, but the effect of 
impure water made this use of it also suspicious. He was 
not aware that it could' be shown that in aggravated cases 
another class of disease might not be produced. In Man- 
chester we can see the accumulation of matter taking place 
in the fog to such an extent that it lies like a cap over the 
whole town, and so increases that every sense is affected, 
whilst the lungs and eyes suffer severely. The matter in 
solution in this case is not putrefactive, although injurious, 
or it would probably sweep us off instantly. Probably no 
accumulation of putrefactive matter equal in amount ever 
occurred in the natural atmosphere. It illustrates, however, 
the mode by which the emanations of the soil are collected 
in the atmosphere and presented in a concentrated form for 
