The ectoparasites of man are, generally speaking, well known, and many of them have been recognized from the earliest times. They are also easily determined, in the main, while, on the other hand, the difficulties to which they give rise are not, as a rule, serious, but yield readily to simple treatment. With the endoparasites, however, the case is precisely the reverse. They are not, as a rule, more than superficially known, and it is only recently that attention has been generally called to their number and the effects often serious which they produce in the human organism.
To be sure, a long series of such forms has been recorded in the past, and the serious effects of their parasitism has been emphasized in some quarters. Thirty years ago Leuckart1 listed thirty-three species which had been found in man, and, in company with Virchow and a long