19, 3 Maxwell: Filariasis in China 263 
Philippines it is known that this periodicity is usually lacking; 
and by the acetic acid concentration method, even where the 
regular periodicity prevails, it is possible to show that microfi- 
lariz are never entirely absent from the peripheral blood. 
What is the cause of this periodicity? To answer that it is 
a provision to enable them to be reached by their intermediate 
host is only to throw the question a step further back. What 
then is the cause that leads them to forsake the periphery during 
the day? Possibly it has to do with the accumulation in the 
body of some chemical substance which, while producing sleep, 
tends to attract the filarize to the periphery. In this connec- 
tion an article by Lynch® is of importance as confirming the 
views of Smith and Rivas that the mechanics of the capillary 
circulation play a large part in the production of filarial perio- 
dicity. He gives details of some experiments with drugs which 
alter the vessel tone. A vasodilator such as nitroglycerine was 
followed by a decrease of the embryos in the peripheral blood, 
while vasoconstrictors such as epinephrin or pituitrin were fol- 
lowed by an increase of these embryos, and a collapsed lung 
in a dog accumulated microfilarie immitis in enormous num- 
bers. 
Their absence from the liver and spleen during the day, 
as proved by the results obtained from aspirating these organs, 
is remarkable.. These results have been completely confirmed 
by the post-mortem examination reported in 1899, by Man- 
son, (26) of the case of a man harboring this parasite who 
committed suicide during the day by swallowing prussic acid. 
In this case the liver and spleen were both practically free 
from embryos, and both of these organs are markedly con- 
cerned with metabolic processes. 
Where do the embryos retire to during the day? In the case 
of suicide above quoted they were found to be distributed as 
follows: : 
TABLE 4.—Distribution of embryos in body of man dying in the daytime. 
Lung Many. 
Large vessels near heart Many. 
Vessels of heart wall Many. 
Brachial ven comites Moderate number. 
Liver Almost absent. 
Spleen Almost absent. 
Brain A few. 
Scrotum None. 
"Lynch, K. M., Filarial periodicity, Journ. Am. Med. Assoc. 73 (1919) 
760. 
