Their respective periodicities are very characteristic; more so, apparently, in the case of mf. loa than in that of mf. bancrofti; for, whereas by inverting the sleeping habits of a subject of F. bancrofti infection it is easy to invert or disturb the periodicity of the microfilariæ, this cannot be done in the case of mf. loa. Unfortunately, I can adduce only one experiment in support of this remarkable circumstance; but that experiment was a very thorough and carefully conducted one, and extended over a considerable period. During all the time the patient (who had had several L. loa excised at different times and who was still showing signs of their presence) slept during the day and kept awake during the night; nevertheless, the microfilariæ
Fig. 155.—L. loa, male. (Partly after Looss.)
continued to appear in vast numbers in the peripheral blood during the day, but were only very rarely found in it during the night.
Although in the fresh liquid blood it is practically impossible to distinguish, with the microscope alone, the living mf. loa from the living mf. bancrofti, in dried and stained films certain more or less pronounced differences can be made out. (1) In such preparations mf. bancrofti is usually disposed in sweeping and graceful curves such as a skilled penman might make (Plate XI., Fig. 1); mf. loa, on the other hand, assumes a stiff, ungraceful, almost angular attitude like the flourishes made by a schoolboy (Plate XI., Fig. 2). (2) The tail end of