FILARIA EMBRYOS IN BLOOD 309 
body of the mosquito. The actual mode of transmission from the mosquito to 
man remained unknown for a long time and gave rise to a variety of conjectures. 
It has been determined only within the last few years. as we shall see farther on. 
The relation of the human parasites of this genus to mosquitoes has been es- 
tablished for several species, although there seems to be some confusion from the 
difficulty of always identifying with certainty the larval filarie. The species 
concerned are: Filaria bancrofti, F. perstans, F. demarquayi and F. philip- 
pinensis. With other species of Filaria investigations and experiments with 
mosquitoes have been entirely negative and these are supposed to have some 
other blood-sucking arthropod for an intermediate host. In addition to certain 
human filariz the transmission by the mosquito has also been proved for Filaria 
immitis of the dog. 
THE FILARIAL WORMS. 
The adult filarie are long, thread-like, transparent worms. The female is con- 
siderably larger than the male. In Filaria bancrofti the female measures from 
85-90 mm. (33—-4;% inches) in length by 0.24-0.25 mm. in diameter; the male 
measures about 40 mm. (1f in.) in length and 0.1 mm. in diameter. 
The adults of Filaria bancrofti, as already stated, live in the lymphatics or in 
the connective tissues of different parts of the body of human beings; the two 
sexes are often side by side, or a number of individuals are associated, and they 
are capable of living there for a long time. When present in the lymphatic 
vessels they may produce serious pathologic conditions, caused, according to 
Manson, by obstructing at certain points the flow of the lymph. This accumu- 
lates and dilates the vessels and lymphatic spaces, and this mechanical dis- 
tension is accompanied by an irritation of the vessels and of the surrounding 
connective tissue. It causes frequently very great swelling, and sometimes 
results in the extraordinary deformities of different parts of the body known as 
elephantiasis arabum. It seems, however, that these effects do not appear until 
long after the infection and it is well known that in elephantiasis the filarie 
are no longer present. Dr. Lebredo particularly points out the abundance of 
the parasites in children and the large number of cases in which marked symp- 
toms of the disease are absent. 
The female Filaria, enclosed in the lymphatic vessels, is viviparous and gives 
birth to an immense number of microscopic embryos. These embryos are eel- 
shaped, enveloped in a loose sheath, and are very active. They spread in the 
lymph and then with it into the blood, and it is in the blood that they are com- 
monly observed 
PERIODICITY OF FILARIE. 
The embryos of Filaria bancrofti are usually in abundance in the blood of the 
peripheral circulation only during the night, or during sleep; during the day, 
or when the patient is awake, they can not be found. There seems to be no good 
explanation of this periodicity, nor is it absolutely exact, but it appears to con- 
