' FACTS IN FILARIASIS. 
405 
periods; we have frequently seen them alive at the end of 
thirty hours. 
We found that the best lens to look for them was one mag¬ 
nifying 100 diameters. 
One word in regard to the so-called involucrum. We 
have never in any quite recent lamina seen a filaria with 
anything resembling an involucrum, nor in any lamina so 
long as the blood retained its perfect fluidity. On the other 
hand, we have invariably seen an involucrum developed by 
the wriggling of the filaria, whensoever (the serum and blood 
globules being squeezed out) it had to plough its way through 
plastic fibrine. We have over and over again, both with low 
and high powers, watched the filaria while swimming free 
and naked in serum, thrust its head into a surrounding film 
of viscid fibrine, and with some effort drew it out again, 
trailing behind it a broad product which it gradually in 
the more liquid serum whisked off as it kept twisting and 
untwisting itself, and this process we have seen repeated half 
a dozen times in as many minutes. The same thing we saw 
happen over and over again with the tail or any other part 
of the body, and still oftener, of course, with the whole body, 
before the fibrine, gradually hardening and contracting, 
squeezed the life out of it. A similar adventitious involucrum 
we can easily believe, though we have not observed it, might 
be formed round the filaria from a very fine film of serum as 
this went on to set. A drop of water allowed to pass under 
the covering glass freed the filaria at once from its involucrum 
were it never so dense, never so extensive. We are, there¬ 
fore, we believe, in a position to affirm that the so-called 
involucrum is no integral part of the filaria, but simply an 
adventitious film of fibrine. 
Like other observers we were struck with the fact that 
the filaria was often exceedingly active for hours in its 
movements. These consisted almost entirely in twisting and 
untwisting itself and not in progressing from one part of the 
slide to another, so much so that, as a general rule, it 
would for hours remain in the field of a high-power lens. Does 
not this depend simply on the fact that, by the fall of the 
covering glass, the filaria has been driven in into a hollow 
between this and the slides, out of which it finds no egress ? 
The few exceptions would seem rather to confirm the truth 
of this hypothesis, showing that the filaria can progress 
where there is room for it to do so. 
The space is necessarily always very shallow, and we 
constantly saw filarids getting caught between the two glasses 
either by the bead or tail or any other part of the body. 
