258 The Philippine Journal of Science 1921 
tions of its victims are still few in number, and there is much 
yet to be worked out concerning its morbid pathology. 
We do not yet know, for example, how long it takes after 
infection before the embryos appear in the blood stream; nor do 
we know why hyperfilariasis does not take place in those who are 
continuously exposed to the bites of infected mosquitoes. We 
do not know how long the adult worms are capable of putting 
forth embryos, nor do we know the true cause of filarial 
periodicity. Occasionally it is possible for the parent worms 
to die as the result of a catastrophe, which may involve the 
human host and cause his severe illness or even death; and if 
this has taken place and the human host has survived, it is 
possible for the latter to become reinfected and again present 
the phenomena of the disease. 
Yet again it is possible for the human host to harbor the 
parasite and present no symptoms of disease at all, the only 
evidence being the presence of the embryos in the circulating 
blood at the proper time. 
The distribution of the disease throughout China is somewhat 
peculiar. Roughly speaking, the infection does not spread north 
of the Yangtse Valley, though individual cases of the disease may 
be met with farther north. These individuals, however, have 
been infected in the southern regions and not in the northern. 
Following the line of the Yangtse River west, the disease is 
found sporadically along both banks and also in Kweichow and 
southern Szechwan, getting less and less frequent as one ascends 
the river. 
Coming back to the coast from the mouth of the Yangtse 
down to the Tonquin border there is a belt some 15 to 25 miles 
(25 to 40 kilometers) broad, and the major portion of the 
disease is found in this coast belt. Most of the islands off the 
coast are also infected, but not heavily. When one passes in- 
land beyond this belt, the infection is practically lost, although 
occasionally a small patch of infection may be found on the 
higher reaches of a river; for it tends to spread upward along 
the banks of all the rivers between the mouth of the Yangtse 
and the Tonquin border, but not to any considerable distance. 
Kiangsi is entirely free, and Fukien away from the coast belt 
is uninfected, and when imported inland, except in the larger 
river vicinities, the disease does not, according to my experience, 
tend to spread. 
The case incidence, of course, varies with the region and, speak- 
ing broadly, increases toward the south and decreases toward 
