I shall suggest presently, some common cause of peripheral origin.
It will be convenient here to consider briefly the absence of filarial embryos in the blood, which is associated with this theory. In a number of cases of elephantiasis an examination of the blood shows the absence of filarial embryos, and it is explained that this is due to the blocking of the lymphatics, the embryos being unable to gain the main lymph stream and thus enter the blood; while the presence of embryos in some cases is got over by suggesting that they are derived from a reinfection. In the first place, this assumes an absolutely impervious obstruction, for, of course, as the embryos can pass through the smallest blood capillaries, they can do so through the smallest lymph capillaries. I think I have shown how very difficult it is to understand how such a complete obstruction as is required can take place.
Then we must remember that in a population which is infected to a greater or less degree by F. nocturna, any disease, whether it be pneumonia or Bright's disease, or eczema or elephantiasis, ought to show an amount of filarial infection equivalent to the general infection of the population. In other words, if there is an infection of 25 per cent, in the general population and 75 per cent, uninfected, we would expect to find at least 75 per cent, uninfected in any given disease. Now, I do not think that it has been conclusively shown that the proportion of uninfected cases in elephantiasis is greatly out of proportion to the uninfected in the general population; we would require to examine a very large number of cases in a district, which has not hitherto been done. The only figures which I have been able to find are those given by Dr. Low, and these vary with the general infection of the population, though at a somewhat lower level. He gives the following results:—
