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Scientific Memoirs by
regarded as either bacterial or infusorial forms, or less probably as zoospores
or possibly as embryos of nemat helminths. Other analogues may exist.1
Comparison with the immature young of nematode worms is alluded to, because it
happens that Dr. Evans once found numerous embryos of a filaria in the blood of a
camel in bad health and associated with four other camels affected with genuine "surra;"
and Mr. Steel also detected in the blood of a mule under experiment a nematode "worm;"
the hæmatozoon under notice being, however, absent in both these instances. I never met
with blood-filariæ in the rat, nor had Dr. Lewis. Micro-filariæ commonly present charac
-ters wholly diverse, being much larger in dimensions, cylindrical or vermiform, non-
flagellate, of granular aspect or showing traces of internal organs, and sometimes enclosed
within a delicate sheath: besides, the direction of movement is not uniform; and it has
not been shown that these temporary tenants of the blood can be reproduced through
inoculation.
As to comparison with spermatic elements, the late Dr. Lewis observed (in his
second Memoir) that he was once inclined to think that the flagellated organisms of the
rat might be the spermatozoa of some parasite hidden in the tissues of the animal; men-
-tioning their amazing similarity to the spermatozoids of a Tænia seen in the intestines of
rat, whose blood, however, was at the time free from organisms. The lateral membrane
of the hæmatozoon would also call to mind the similar appendage of spermatic filaments
perhaps elsewhere present than in certain lizards. But all such filaments move the thick
end foremost, their flagellum being a propeller; and, besides, they are not independent
organisms capable of reproduction per se.
The bacterial character of these blood-parasites is disproved by their non-cellular aspect,
and by their contractile plasma in which rapid changes of length and thickness are seen wholly
unknown amongst the algoid filaments: moreover, their prompt decay after a few hours'
keeping, with entire absence of signs of reproduction by division or spores, would nega
-tive such view. Perhaps the nearest approach to resemblance would be with the spirillum
(or spirochæta) of human relapsing fever, which I mention because it has been alluded to
by several observers as regards appearances in the fresh blood of rats and equines, and has
in the latter instance led to the organisms being designated as "spirilloids;" Mr. Steel's
term seeming the more warrantable, since he found a distinctly recurring pyrexia to attend
the presence of the organisms in mules and in animals infected from them. I could myself
compare directly the living human parasite with that of the rat, finding no other than an
incidental similarity in a peculiar twirling displacement of the red blood-discs, caused by
movements of the active organisms present; watching for a time, indeed, both kinds of
organisms ceased to move, and becoming rigid drifted away towards the sides of the con-
-taining cell, when all resemblance ended; the spirochæta retaining its spiral form, speedily
enlarging much and joining with other filaments to form a close network which at its nodes
finally blends into a uniform granular, zooglœa-like clump. The contrast here, even so far,
with what has been described above of the rat-organisms, is sufficiently marked to indicate
an essential difference in their nature: there being manifest, under similar conditions, a
1
I had purposely omitted in the text any allusion to the so-termed 'hæmatozoa of malaria,' which,
after Dr. Laveran and others have been recently recognised by Prof. W. Osler, and by him are in a certain
sense associated with the organisms of ' surra' equines and of the rat. This omission was due to the
absence of a personal knowledge of the blood-parasites often present in the febrile human subject; and
having, since the text was despatched from Bombay, acquired some practical information here, I hope to be
allowed to make good the defect in a later Note below.