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6 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
phenomena of malaria were unsatisfactory and insusceptible of 
scientific demonstration. 
' According to the best medical authorities the most generally 
admitted facts upon which the present orthodox theory of malaria 
rests were as follows: 1. Malaria affects by preference low and 
moist localities. 2. It is almost never developed at a lower tem- 
perature than 60° F. 3. Its evolution or active agency is checked 
by a temperature of 32° F. 4. It is most abundant and most 
virulent as we approach the equator and the sea-coast. 5. It has 
an affinity for dense foliage, which has the power of accumu- 
lating it, when lying in the course of winds blowing from malarious 
localities. 6. Forests or even woods have the power of obstructing 
and preventing its transmission under these circumstances. 7. By 
atmospheric currents it is capable of being transported to consider- 
able distances—probably as far as five miles. 8. It may be devel- 
oped in previously healthy places by turning up of the soil, as in 
making excavations for the foundations of houses, tracks for rail- 
roads, and beds for canals. 9. In certain countries it seems to be 
attracted and absorbed by bodies of water lying in the course of 
such winds as waft it from the miasmatic source. 10. Experience 
alone can enable us to decide as to the presence or absence of 
malaria in any given locality. 11. In proportion as countries, 
previously malarious, are cleared up and thickly settled, periodical 
fevers disappear, in many instances to be replaced by typhoid 
fever (?) 12. Malaria usually keeps near the surface of the earth. 
It is said to “hug the ground,” or “love the ground.” 13. It is 
most dangerous when the sun is down, and seems almost inert 
during the day. 14. The danger of exposure after sunset is greatly 
increased by the person exposed sleeping in the night air. 15, Of 
all human races the white is most sensitive to marsh fevers, the 
black least so. 16. In malarial districts the use of fire, both in- 
doors and to those who sleep out, affords a comparative security 
against malarial disease. 17. The air of cities in some way renders 
the poison innocuous; for, though a malarial disease may be raging 
outside, it does not penetrate far into their interior. 18. Malarial 
diseases are most prevalent towards the latter part of summer and 
in the autumn. 19. Malaria is arrested not only by trees, but also 
by walls, fences, hills, rows of houses, canvas curtains, gauze veils, 
mosquito nets, and probably by fishing nets. 20. Malaria spares 
no age, but it affects infants much less frequently than adults. 
