THE MICROBES OF HUMAN DISEASES. 181 
to the south-east of the town of Lancaster, and the 
neighbouring valleys are low and damp. The third 
quarter of the town, touching on this meadow, and 
all that part which is not raised from 35 to 40 feet 
above the level of the meadow, have always been 
districts in which attacks of intermittent fever are 
prevalent. Those who live near the marsh are liable 
to annual attacks of fever from May to November. 
In August and September these attacks are generally 
the most severe.” 
We said that moisture does not favour the trans- 
port of microbes and their spores through the air, 
but the remark does not apply to fogs, in which 
numerous spores are found. We know that fogs are 
formed of minute globules of water, which float in 
the atmosphere, and of which the vapour of our 
breath, only visible in cold weather, can give us an 
idea, These globules of water float in the air just as 
spores and all kinds of dust do, without wetting 
the spores or running together, since as soon as this 
occurs, the fog ceases to be; it is condensed, and falls 
in.the form of more or less fine rain. Salisbury has 
ascertained that there is a certain connection between 
fogs and intermittent fevers, and this explains why 
people are more apt to contract fever in the morning 
and evening, at which times there is in summer always 
a fog floating to a varying height above marshy places. 
Tn a farm near Lancaster, the farmer and his wife, who 
slept on the first floor, were attacked by tertian fever, 
