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8 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
Cases were found both near the sea and some two hundred and fifty miles up 
the river at practically the end of British territory. There was no evidence to show, 
that natives living in any particular type of locality were especially subject to infection, 
neither do we find that the disease occurs in well-marked zones or 'belts.' For 
instance, although three cases of infection were found in thirty-five natives examined, 
at Lammin, the natives of similarly situated villages, both neighbouring and distant, 
have been searched in a far more thorough manner and have failed to disclose a single 
parasite. We have found cases in low-lying, river-side villages surrounded by man- 
grove swamps; we have seen them in towns built on high ground and far from 
water, and observed them both near the sea coast and as far inland as Fatotenda. 
How far the disease extends beyond the colony of the Gambia we are unable to say, 
since only twice have we been able to examine natives in immediately adjacent French 
territory.* 
Prevalence 
We saw altogether six cases of trypanosomiasis in the native, and once found 
the parasite in the blood of a quadroon, who can almost be considered a European, 
since his boyhood and a large part of his life were spent in England. 
We examined altogether one thousand and forty-three persons in the Gambia. 
The percentage of infection given by these figures is, we are convinced, smaller than 
is actually the case. 
Our reasons for holding this opinion are the following: — 
(1) Many cases have certainly escaped identification both because of the scanty 
numbers in which the parasites are ordinarily seen in human beings and because of 
the periodicity with which even these are absent from the peripheral circulation. 1+ ' I5 ' 50 
(2) The majority of the natives examined were apparently healthy children 
and young adults, who could be persuaded by small bribes to allow their fingers to be 
pricked. It was in many places extremely difficult to obtain blood from older persons 
who are possibly more frequently infected. In any case the total number of examina- 
tions is too small to permit one to make a dogmatic assertion as to the percentage of 
infection existing among the Gambian natives. 
Symptoms 
Since in both East 5 and West Africa natives infected with trypanosomes have 
shown few or no symptoms ; and since a few Europeans in whose blood the parasites 
have been demonstrated have all suffered in roughly the same way, we think that it 
will be well to describe the cases observed by us in the Gambia according to the race 
of the individual affected. 
* We examined the blood of some two hundred and thirty individuals while at Dakar and St. Louis. Seventy-five were 
hospital patients who had come from various parts of Senegal and the Soudan ; the remainder w ere children — the great majority 
of them inhabitants of St. Louis. Twenty-eight of the hospital patients were white, the remainder Africans. The European 
cases, usually invalided for malaria, were examined with especial care. In the fresh preparations from these cases no trypanosomes 
were seen. The stained films taken from each individual have not vet been searched. 
