298 PHALBN AND NICHOLS. 



IV. THE PARASITE. 



The filarial embryos present in the blood of these patients were studied 

 both in fresh preparations and by appropriate staining. The parasites,, 

 so far as we could make out, were of one variety; the chief features are 

 as follows: 



Motility. — In fresh specimens of the infected blood, the parasite was observed 

 to have the usual wriggling, lashing movements, which changed its position, 

 but which could not be called progressive as the movement was accomplished 

 in no orderly manner. It was only by observing that the lashing movements 

 eventually removed the parasite from the field of the microscope that any 

 change of position could be determined. 



Size. — The average length of the microfilaria in the fresh preparation is 

 about 0.300 millimeter and in stained specimens about 0.270 millimeter. The 

 average diameter is 0.007 millimeter. 



Head. — The head is smooth and hemispherical, surrounded by a notched prepuce 

 having five or six notches. Upon the anterior end of the head is a slightly 

 refractive spot, from which at times is projected forward a short, needle-like 

 process, which is as quickly withdrawn. 



Tail. — The tail slopes gradually to a very fine point. 



Body. — The body is cylindrical for the greater part of its length, and is 

 marked by the anterior V spot, the central viseus and the posterior V spot. 



The anterior V spot is a triangular area, highly refractive, occupying one 

 side of the worm, 0.090 millimeter, on an average, from the anterior extremity. 



The central viseus is situated in the posterior part of the central third of 

 the body. It is granular in appearance, but upon focussing carefully a con- 

 voluted tube can be seen to occupy this granular mass. The length of the 

 central viseus is about 0.040 millimeter. 



Posterior V spot. — We were unable to do more than to make out the 

 presence of such an organ, and were not able to distinguish any details of 

 the structure. 



By appropriate staining, a granular, central column is shown occupying the 

 center of the entire length of the worm. This column is broken by occasional 

 unstained areas. The only one which showed at all constantly was situated in 

 front of the anterior V spot, from 0.055 to 0.060 millimeter from the anterior 

 extremity. 



The stains which gave the best results in the embryo were gentian violet, 

 Bismarck brown and hematoxylin in weak solutions, Borrell's blue and poly- 

 chrome methylene blue. The latter two, mixed with glycerin, each gave ex- 

 cellent results, not only staining the parasite, but preserving its size and 

 appearance as in fresh specimens. 



Sheath. — The embryo has a sheath which exceeds the length of its occupant 

 by one-third to one-half of the latter, but which appears to be tightly applied 

 to the body laterally. Ordinarily it may be observed as a fine flagellum at 

 either end of the embryo, but at times may be seen as a flattened band. 

 Stained specimens show the size and shape of the sheath very well. No move- 

 ment of the filaria within the sheath has been observed. 



Periodicity. — While it was not possible to obtain day and night specimens 

 of blood from all of the cases, a sufficient number were examined at different 

 hours to show that a nocturnal periodicity was the rule. The following table 



