of its transmission from the mosquito to the human host have been worked out and the presence of other blood worms has been demonstrated. But the knowledge of the actual mechanism by which the F. nocturna is said to produce disease remains much the same as it was twenty-five years ago, and I propose to examine briefly the reasons for and against the opinion that F. nocturna is the causal agent in producing the diseases which I have enumerated, especially elephantiasis. And it is important to remember that in the 'seventies, when this theory took its rise, the extensive geographical distribution of F. nocturna was not well known, as well as the very great variations in the amount of the relative infection of different peoples, and it was not an unnatural conclusion that this worm, whose habitat was the lymphatics, which was found in tropical countries, in which also a disease of the lymphatics, namely, elephantiasis, was common, a disease clearly associated with some form of obstruction of the lymphatics, was the causal agent in producing this and other similar diseases. And it has been generally assumed that this is the correct view, and considerable ingenuity has be3n shown in explaining the difficulties which have from time to time cropped up. I propose, then, for the sake of argument, to assume that elephantiasis is not due to filaria, to criticise as impartially as possible the various suggestions put forward, to examine the possible mechanism of its production, and to see whether, if possible, there is not another explanation which would account for the production of this and other so-called filarial diseases.
Now the argument relied on in favour of the causal relationship between F. nocturna and filarial diseases are mainly two:—
- 1. That the geographical distribution of endemic elephantiasis and F. nocturna coincide, and
- 2. That F. bancrofti is a parasite whose habitat is the
