MALARIA EXPEDITION TO NIGERIA 67 
able to find any record of a case or cases in which the embryos were regularly 
counted for a period shortly before death and in which, post-mortem, adults were 
tound. 
In the examination for malarial parasites' of blood specimens from a large 
number of native children of all ages up to about 1 8 years, we encountered a 
single filarial embryo only, in one case (specimens taken during the day were examined 
only) — aged 1 1 years, out of 390 cases. In view of the number ot adults infected 
with F. diurna in the same districts, this is remarkable and further tends to support 
the idea that, the extent of infection increases during the period of childhood, 
until, when adult age is reached, there are a sufficient number ot mature female 
filariae in the body to give an observable number of embryos in peripheral blood 
during the usual examination for microscopical purposes. 
Under any other circumstances, it seems to us, there would be no chance of 
an escape from the continued and renewed infection of every individual. In a 
certain district, were such a number of embryos observable in the blood of every 
child — or even of a similar percentage ot children, as is presented by the adults, 
every mosquito of the species capable of acting as intermediary hosts would become 
infected and in consequence every man, woman and child in that district would 
become infected to such an extent as to exhibit embryos in the peripheral blood. 
It thus seems that in this way nature has placed a limit to the prevalence of this 
infection. 
Filaria perstans 
But little need be said of the periodicity of this worm, which persists in the 
peripheral blood throughout the whole of the day. The following table illustrates 
the phenomenon. 
I. Report of the Liverpool Malaria Expedition to Nigeria. Liverpool, 1901, part i, p. 1 1 et seq. 
