Distribution of Tropical Diseases in Africa. 445 
Exposure, intemperance, bodily or mental depression, may 
result in ardent fever, with cerebral or hepatic complications. 
Dysentery and diarrhcea occur chiefly when the water-supply 
is impure from storage or contamination with decaying organic 
matter. 
The chief diseases met with during the hot season are 
ophthalmia, dysentery, intermittent fever, rheumatism, 
leprosy, guinea-worm, and prickly heat. 
The rainy season is far more unhealthy than the hot 
months, especially at its commencement, and to a less extent 
at its close. The temperature of the air falls at the beginning 
of the rains, producing a feeling of vigour after the intense 
heat; but the moist atmosphere, combined with the sun’s 
rays, greatly increases the perspiration, and along with this 
there is relaxation of the muscular system, with cardiac 
debility and congestion of the internal organs. Should the 
rainfall be scanty, irregular, and alternating with hot 
weather, severe outbreaks of fever are to be expected from 
the formation of pools of stagnant water rich in organic 
matter. Dysentery and diarrhcea are also prevalent from 
the contamination of the water-supply; while in addition to 
the diseases mentioned above, diseases of the respiratory 
system are also met with. 
It is likewise to be noted that though guinea-worm may 
occur at any season of the year, it seems to be more trouble- 
some during the colder months. Elephantiasis and goitre 
also seem to commence more frequently in the cold season, 
though afterwards the seasonal influence on their progress is 
less marked. 
The season of the harmattan is the most healthy part of 
the year, the drying action of the wind stopping the decom- 
position of vegetable matter, and thus the production of 
malaria. When it begins, patients suffering from malaria 
rapidly become convalescent, while other diseases are fre- 
quently benefited in like manner. The dry, cold air, while 
it braces up the body generally, reddens the skin and renders 
it dry and harsh. The nostrils and pharynx become dry, the 
lips chap, and the eyes may become inflamed. The sensible 
perspiration is almost arrested, and the activity of the kidneys 
