Filarial Periodicity

A most interesting phenomenon in blood parasitology and one of practical importance in the question of transmission of the parasite, is the periodicity of filariae. This term has come to mean a periodic increase in numbers in peripheral capillary blood of the embryos of filariae. This, in the case ofFilaria bancrofti, occurs during the hours of sleep, and ofFilaria loa, during the hours of activity. Until Smith and Rivas1developed the acetic acid concentration method of counting the number of microfilariae in a given amount of blood, "filarial periodicity" signified the periodic appearance and disappearance of microfilariae in the peripheral blood. This acetic acid concentration method of examining for microfilariae has brought about important changes in our conception of the phenomenon, and has opened a new avenue of approach to the problem. Smith and Rivas have thus been enabled to show that filaria embryos are to be