118 Mr. T. Hopkins's Observations on Malaria. 



That malaria fever is an effect of an excess of steam in the 

 atmosphere, more especially when the temperature is not con- 

 siderably above the dew-point, may be inferred from various 

 observed circumstances. In the neighbourhood of Rome, as 

 soonas the morningsun has raised thetemperature, danger from 

 malaria is much reduced. On the 10th of August the stub- 

 ble and weeds of theCampagna are begun to be burnt, and it 

 is found that whenever the heat from these fires raises the 

 temperature, the air is for the time partially purified ; doubt- 

 less because this heat, like that of the sun in the morning, dries 

 the air as well as heats it; that is, raises the temperature to a 

 oreater height above the dew-point. It is a common remark 

 in the Campagna, that keeping up a fire in a house during 

 the nifht purifies the air; and it is well known that in those 

 parts of Rome where the poor people are crov/ded together 

 there is no malaria, while the thinly inhabited parts are af- 

 fected. In order to avoid malaria, the wealthy Italians are 

 careful not to sleep on a ground floor. And any one who 

 has observed the way in which a fog rising from a neighbour- 

 ing marsh or lake creeps along and spreads itself over the 

 lower levels, even when the air appears to be still, will see 

 why rooms of ground floors should be filled with damp air in 

 certain places. The ancient inhabitants of Italy, as may be 

 seen at Pompeii, built their houses round an interior square, 

 the entrance to which could be easily closed ; this enabled 

 them effectually to keep out a low stratum of damp air. The 

 streams of fog creeping along the ground as they do, enable 

 us to account also for the local attacks of malaria. A slight 

 current of air confined or turned by a valley, a ridge, a wall, 

 or even a hedge, may take the vapour to a particular part, 

 while other parts, at a small distance , may not be visited by 

 it. The supply iDcing continued from the source, the vapour 

 may be sufficiently dense in certain parts to make those parts 

 unhealthy ; but when it expands and by its elastic force diffuses 

 itself, it becomes too thin to saturate the adjoining air up to an 

 unhealthy degree. The same kind of observation will apply to 

 planting woods, or even hedges in particular situations ; they 

 may by arresting or turning the sluggish currents of saturated 

 air become barriers. It is said that malaria is never found 

 more than 2500 feet above the level of the sea ; this may arise 

 either from the lowness of the dew-point, or the absence of 

 that density of steam which exists only in the lower regions 

 of the atmosphere. 



The difference observable between the natives of a warm 

 and damp country, and strangers coming to it from a colder 

 climate, in their respective capabilities of resisting malaria is 



