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66 THOMPSON YATES LABORATORIES REPORT 
For instance, in Cases 3, 4, and 5, the numbers at each examination are as near as 
would be expected ; but in Gases 1 and 1 the variations from day to day are 
considerable. 
In the above tables, III to XI inclusive, a further feature is to be observed, 
namely, the variety in the severity of the filarial infection : thus, taking the numbers 
of embryos at the period when they reach a maximum in peripheral blood, it is seen 
that they are included between 3' and 480 in three specimens, or 1 and 160 per 
specimen of blood. It surely follows, then, that in some natives even when they are at 
their maximum number, in the peripheral blood, they may still be too few, in to to, to be 
observed in a single preparation of blood. Consequently, many more natives must be 
habitats for filariae than is supposed from the observation of peripheral blood in the 
usual way. When treating of F. perstans (see Table XII, Case 4), it will be seen that in 
some sixty preparations of the blood of one case, one filaria only was observed (possibly 
the infection with F. perstans, or the maturation of the parasite, may have occurred 
during the month under which the case was under observation). MansonV figures shew 
the same features in the cases of undoubted F. nocturna infection ; but few of these 
figures, however, give the number of embryos per drop of blood when the largest 
number would have been present in peripheral blood, namely, twelve midnight : most 
ot the specimens were made not later than ten p.m. : the figures range between 1 and 105. 
These facts must be taken to give some indication of the severity of the infection, of 
the number of adult females in the organism : since the results of observations 
extended over a long period — a month or more — shew no decided periods of increased 
fertility. But it surely must not be inferred from the relative numbers of embryos 
in the two extreme cases that the number of adult females in one case is a hundred 
or more times as many as in another, although it is difficult, at the present stage 
of our knowledge, to understand why such an inference should not be drawn. 
Referring to this subject, Manson 2 is reported to have said — ' If anyone is fool- 
hardy enough to submit to be bitten by filariated mosquitoes, and if subsequently 
no young filariae be found in the blood, it must not be concluded from this that a 
mosquito bite is not the medium of infection. My belief is that before embryos can 
be found in the blood by ordinary miscroscopic observation large numbers of parent 
filariae must be present in the lymphatics. In many cases we know that hundreds of 
parent filariae are present. Thus in one case only two or three embryo filariae are 
found in each drop of blood ; in other instances as many as 600 or more are found 
in a drop implying the presence of 300 times as many parental worms.' Although 
as above stated we do not at present understand why such an inference cannot be 
deduced, it is evidently not justifiable to make such an inference, judging from the 
number of infected inhabitants and the extent of their infection. We have not been 
1. Manson, The Filaria Sanguinis hominis. London, 1883. 
3. Manson, Brit. Med. Journal, Sept. I. 1900. P. 536 
