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might at a red corpuscle endeavouring to detach it from its rouleau. "When the
parasites are " numerous and active," we see them all over the field directly we get
the focus; most active in their movements, they pass from place to place by lashing
their long thin bodies, by an eel-like movement, and in a vermiform manner by the
propagation of a body-thickening along them like a wave. They may be seen free in
the pools of serum between the rouleaux or firmly attached to a corpuscle or two
which they have succeeded in appropriating and drag after them as they move back-
wards, spin round and round, shake and worry or occasionally push forwards with
rapidity. These artificially motile red corpuscles move into and out of focus rapidly
and especially attract notice. At first I thought them the heads of the parasite as
they were sometimes distinctly heart-shaped, but enlarged experience very soon proved
that it was not so, the heart-shaped ones being merely two corpuscles simultaneously
detached from the end of a rouleau. Dr. Evans' graphic description of the actions
and appearance of the surra organism applies to these to a very great extent, but not
entirely. As he mentions, they always take hold of the corpuscle by their blunt ends,
sometimes several at a time to one corpuscle, then they move backwards, tugging
hard. I have frequently seen two or three of the parasites tugging together at one
piece of corpuscle, and they often become entangled, several together, in one wriggling
mass. I have never been able to observe what Ignatovsky of Odessa points out that
these agglomerations may be observed exclusively at the end of the attacks and that
the number of balls or bundles of the spirilloids invariably increases as the moment of
critical perspiration approaches, but then we have no sudorific crisis in mules.
However the bundles of spirilloids are well marked in some of my stained specimens.
At different times the organisms differ in size, and I have even noted large and small
side by side in the field of vision. In a number of observations we shall find them
sluggish or active, large or small, ferocious or placid, altogether in every condition
suitable for examination of their structure and actions. Under a powerful light they
are refrangent, irregularly-curled lines ; under moderate light each looks like a very
thin black line actively motile in such a way as to give it a subspiral appearance, but
not uniform in thickness throughout. Although, as described, they generally move
in the direction of the blunt end, except when dragging at the corpuscles, a bold
stroke with the lash-like tail or a doubling of the parasite on itself until the tip of the
tail almost meets the blunt end followed by a sudden straightening may cause lateral
movement. I have never seen them attack the white corpuscles, nor, indeed, any
constituent except the red ones, which sometimes seem to be torn in pieces by two or
more parasites; fragments may be seen in most specimens taken towards the end of
the relapse, but we must not consider as such some corpuscles shaped like a quarter
moon, which, on careful examination, prove to be unbroken red corpuscles altered in
shape. At first I found that the parasites were no longer detectable in specimens
after drying, and this serious difficulty presented itself until, on Dr. Vandyke Carter's
advice, I adopted the Weigert-Koch method of drying in very thin layer on a cover
glass. Even then they could be seen only with great difficulty, and the conclusions
obtained were not reliable. I tried various staining agents and at last had complete
success with aniline dyes. The effect of obtaining the parasite stained and quiet is
remarkable in its modifying influence on our preconceived ideas as to its general
characters. The parasite in motion is as different in appearance from when at rest as a
rapidly revolving wheel is from a still one. It is only when this fact is realized that
we are able to understand how it is that competent observers figure the same object
so differently as they have 8pirochæta obermeieri. This will be seen by comparison
of the figures of Koch and Ziegler here inserted (as kindly copied for me by Veteri-
nary Surgeon F. Smith)—vide opposite page. It will be noted how in some diagrams
we see organisms with well-marked spiral figure, uniform in thickness throughout and
remarkably long in relation to their width. This is the idea conveyed on first sight
by the equine parasite in motion. In other diagrams we find that these little beings are
represented as having a much less spiral figure (although still this feature of their
shape is well marked) and as markedly tapering towards each extremity, altogether
looking very unlike the long spiral thread figured by the other observer. Certainly
the difference between the living and the dead parasite is extremely striking. These
will contrast excellently with my diagrams of the parasites of the mule taken before and
after staining. The former must be received with reserve, because it is a most difficult