THE MICROBES OF HUMAN DISEASES. 181 



to the south-east of the to\*n 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. 

 In a farm near Lancaster, the firmer and his wife, who 

 slept on the first floor, were attacked by tertian fever, 



