Distribution of Tropical Diseases in A frica. 469 
to blister the surface, and dress the blister with morphia ; 
and if the internal administration of belladonna does not 
succeed in controlling the pain, the following prescription 
should be tried,— 
kk. Nitrate of potash, 40 grs. 
Spirits of sweet nitre, 2 drs. 
Colchicum wine, 2 drs. 
Water to 8 ozs. 
1 oz. thrice daily. 
Guinea- Worm. 
(Filaria Medinensis ; Dracunculus Medinensis.) 
The guinea-worm is a nematoid worm, the female only of 
which is known. It is about 1 mm. thick, and has an average 
of 2 feet in length; it may, however, be much longer. It is 
cylindrical; the anterior extremity is rounded, and presents 
a small depression surrounded by an elliptical chitinous 
plate, at the margin of which are two papille. The posterior 
end is a short curved point; it is opaque, of a milk-white 
colour, and on each side there is a longitudinal line. The 
interior of the worm contains an immense number of young 
filaria in an acrid secretion. The tenacity of the tissue of 
the guinea-worm is considerable, so that a loop of the 
parasite will support the weight of 10 oz. 
The largest number of persons becomes infested with this 
worm at the end of the rainy season, or in the hot season after- 
wards. The guinea-worm attacks all races and nationalities, 
both sexes, and at all periods of life. Usually only one or 
two worms are found in the patient, but I once saw one with 
no less than forty-two worms. It is said to gain an entrance 
into the body by means of drinking water, but this is doubtful. 
So far as I know, there is no case on record in which the worm 
has been found within the abdomen. It is in all probability 
deposited beneath the skin, and this theory is supported by 
the fact that it only occurs in those who walk bare-footed 
either constantly or occasionally, that it principally occurs in 
the lower extremities, that in those cases in which it occurs 
on the trunk or arms it is in persons who have slept on the 
