70
Shape.—It has an apparently round body when it is fresh and active, which tapers
in front forming a neck ending in a blunt head, and behind it has a tapering tail from
which there extends a long slender lash, so fine that it can seldom be seen: its outline
can be made out sometimes for an instant when its motion in the serum refracts light,
but its presence may be inferred from seeing the corpuscles quivering at a distance from
the visible part of the tail. Sometimes the head appears a very little thicker than the
neck, but, as a rule, I failed to see any difference, and sometimes I thought it looked
smaller; probably its size is not always the same relatively. In one or two instances,
one particularly, when the body was sunk in the serum, and the head facing towards the
covering glass, I saw what appeared like a circlet of short hair-like pseudopods. I only
saw it for a few seconds, as the head sank out of focus, and I was not able to make a
reliable observation, but I mention it in order that my impression may be corrected or
confirmed by future observers. When it dies slowly in serum, its body flattens out
After many hours of watching it closely in all its changes of form and movements, I
came to the conclusion that it has two fin-like papillae on each side, one near where the
neck begins and one near where the tail begins. In only very few instances was I able
to see the four at once ; but whether I saw one, or two, or three, they were always in
the same relative positions. Sometimes they could be seen projecting out from the
body, at other times they were seen as refracting spots on the body. Perhaps they
are pseudopods also.
35. Motion.—Undulatory, eel-like, and as a rule wonderfully active. The body
alters its shape in its movements, shortening and thickening, lengthening and becoming
more slender, so that it is most difficult to estimate its true size. Its progress is almost
always in the direction of the blunt end, which I therefore call the head, though it
goes in the reverse direction sometimes when pulling at a corpuscle.
Size.—Its visible length ordinarily appears on the average to be about three or
four times the diameter of a white corpuscle, and the average diameter of its body
about one-eighth or one-tenth that of a white corpuscle. That is how it appeared to
me and others, but I had no micrometer to measure it with. There is much of its
tail end that is not ordinarily visible.
Color.—White, like a spermatozoon.
Actions.—It has a wonderful elective affinity for the red corpuscles, but none
for the white, as seen when there are many of the latter in the field. At a certain
stage of its development it is constantly worrying the red corpuscles. The first
exclamation made by every one who saw it at that stage was to this effect: " 0 the
little villains! see how ferociously they attack the red corpuscles." Dr. Haig remarked
that, whatever family it belongs to, its most appropriate specific designation is ferox.
I mention this because to one who sees them for the first time in this stage the
apparent ferocity is a most impressive and distinguishing characteristic. They always
fasten to the red corpuscles by their blunt end, never by any other part, so that it
is not an accidental attachment. They look as if they went to the corpuscle for a
definite purpose, fasten to it, and shake it about in the serum in a very wonderful
manner. I have often seen two fasten to one corpuscle, pull it out of shape, and one
of them would break a particle off, then go about with the fragment, which made it
look something like a bull-headed spermatozoon. On one occasion I saw four of
them fasten to one corpuscle, and pull in contrary directions for some time until they
broke it up. When they thus fasten to a corpuscle they seem to tug hard at it, and
then they lash their tails with unusual rapidity. I have seen them pull a corpuscle
right across the field, and one I saw doing so backwards a considerable distance against
the stream when the stage was inclined; but, as a rule, they move forwards. Some-
times when they go off with a fragment of corpuscle, they wriggle in all manner of
vermicular contortions, as if they wished to get rid of it. When the corpuscles are
in rouleaux the parasites crawl over them and seem to try to push between them.
In this way they often separate the end corpuscles of the rouleaux from the others.
They show a great preference to the concave part of the disk rather than the edge.
What their object is in fastening to the corpuscles I cannot tell, but it is strongly
suggestive of sucking. I have frequently seen one of them suddenly turn aside
towards another, and, I sometimes thought, bring him to by whipping his tail round him
and then fasten to him lengthwise. After that both would wriggle about very actively
together, and look like one long body, I have not been able, owing to their rapid