692
FILARIASIS
[CHAP.
efforts to escape. After a time, the majority succeed in effecting a breach and in wriggling themselves free from the sheaths which had hitherto enclosed them (Fig. 101).[1] The microfilaria now swims free in the blood, the character of its movements once more undergoing a remarkable change. Hitherto, though active enough in wriggling about, the parasite did not materially change its position on the slide; but
Fig. 102.—Section of thoracic muscles of mosquito, showing microfilariæ between the fibres: first day after the insect has fed on a filariated patient. (From a microphotograph by Mr. Spitta.)
now, having become free, it moves about from place to place—locomotes, in fact. If we dissect a mos-
- ↑ This casting of its sheath by the microfilaria can be induced in ordinary blood slides by chilling them on ice, or by otherwise bringing about the diffusion of the hæmoglobin. The following method is usually successful: Ring with vaseline the cover-glasses of several ordinary wet preparations of finger blood obtained at night from a filarial patient; wrap the preparations separately in filter paper and lay them, enclosed in a watertight tin box, on a block of ice for six or eight hours—say overnight. Next morning examine them with the microscope. It will be found, as the chilled slides warm up, that wherever on the slides the hæmoglobin has become diffused and the blood laky, the microfilariæ, as they gradually revive from the chilling, begin to endeavour to break through their sheaths. By evening most of them have effected this, and their empty sheaths can be seen lying scattered about in the viscid blood. The blood must not be frozen.
