NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
( 73 )
along the edge of the plate, standing upright. Next, in the
same way, apply the cement to one edge and one end of each
of the shorter strips, and fix them in position in the same way
one by one. Lastly, cement one edge and the end of one face
of the fourth side, and place it in position, and the tray is com-
pleted. I describe the method of making these trays thus
minutely, as their use is of some importance in the diagnosis of
doubtful cases, as, owing to the lively movements of the embryos,
it is much more easy to detect them in a cultivation than
to find the ova in the fæces. Moreover, a simple pocket
lens, of one inch focal length, affords quite sufficient
magnification, so that a comparatively large amount of
material can be searched over in a few minutes. A good light
is necessary, however, so that, unless a regular dissecting stand
be available, it will be necessary to improvise one, to do which
the tray should be placed over a hole in one side of a cigar-box,
the lid being removed, and a shaving-glass, arranged at a suit-
able angle, placed within the box. The lens may be sup-
ported on a pen-holder fixed in a hole in the back of the
box and thrust through the small holes which are found in
the sides of the horn case of pocket lenses of the usual
pattern. Such an apparatus can be constructed by any one,
however little of an amateur mechanic he may be, and forms
by far the most certain method of diagnosing the presence of
the parasite, when present in only small numbers, and by its
means I have again and again, detected the presence of a few
parasites where repeated careful examination of the fæces for
ova had failed. For a reason that will presently appear, the
cultivation should be allowed to stand for six or eight days
before condemning it as sterile.
On account, then, of the impossibility of keeping the
embryos under continuous observation, I am unable to afford
any exact information as to the number of ecdyses, but where
development is rapid, I estimate the changes of skin at not
less than, twice a day. I have often watched the process, and
some very curious appearances occasionally present them-
selves, as the worm often remains for a considerable time
partially entangled in the old skin.
In every instance that I have watched, the old skin is
ruptured near the head, a small cap of the anterior part of
the chitinous investment being forced off, while the rest of
it is cast off entire, the worm drawing itself out like the finger
from a glove, the tail being the last part freed.
Even in one and the same cultivation, the rate of growth
G
( 74 )
varies greatly, depending no doubt on variations of the amount
of available food supply in different portions of it. In experi-
ments conducted at Shillong, under conditions as nearly as
possible approaching those found in actual practice, the whole of
the stages from ovum to the adult rhabditis stage, to be presently
described, occupied six days. In this case the fæcai matter
was simply spread over a patch of garden soil enclosed with-
in four planks. In experiments conducted in glass vessels,
with a necessarily somewhat restricted supply of air, the de-
velopment takes a trifle longer. The most important factor,
however, is the proportion of fæcal matter, or, in other words,
of nutritive material used. In large fæcal masses, in the
temperature of the plains, fully developed rhabdites may be
found as early as the fourth day. On the other hand, imma-
ture forms may still be found as late as the tenth or even
twelfth day after hatching out.
The first change that takes place is that the cells lining
the intestinal canal proper swell out and become granular,
bulging out into the lumen of the channel, so that its course,
as seen in optical section, appears zigzag. Certain of the cells
at its commencement, i.e., immediately below the hinder bulb,
take on a special development, and remain larger than the
rest throughout life. They probably function as a liver.
After one or two changes of skin, the anterior dilatation of
the oesophagus becomes much more distinct. Between it and
the hinder bulb, a nervous centre, consisting of four or five
ganglion cells, encircling the oesophagus, makes its appear-
ance, and lastly, about midway along the ventral aspect of the
body, there appears a single hyaline cell, the rudiment of the
future generative organs. In these early stages, the mouth
is a simple, somewhat funnel-shaped opening, without either
lips or armature of any kind. The anus opens on the ventral
side of the body, a little in front of the pointed end of the tail.
Almost up to the assumption of the adult rhabditis stage,
the changes occurring at each change of skin are very gradual,
and consist merely of growth of the parts that have already
appeared, 110 further change taking place in the development
of the generative organs until this great and final stage.
In these final changes the worms become adult male and
female organisms, and immediately commence to propagate the
species.
For the benefit of such of my readers as may be unac-
quainted with the details of nematode terminology, it may be
well here to explain what is meant by a rhabditis stage.
( 75 )
Its meaning is that certain parasite nematodes* present the
phenomenon of alternations of generations, the ova laid by
worms in the parasitic stage, developing, not into animals like
themselves, but into a form which no naturalist would place
even in the same genus. In fact, if we were ignorant of their
origin, these forms would find their place, for purposes of classi-
fication, in Dujardin's genus Rhabditis. The worms in this
stage live free, and are in no sense parasites, but when they
reach sexual maturity, they give birth to a generation which
again takes up a parasitic mode of life, or, at any rate, is capable
of doing so, while, as far as can be seen, the first generation
would be incapable of becoming parasitic.
Thus, the worms of such species, in the parasitic stage,
are not the children, but the grandchildren of parasites. In
the present instance, the free or rhabditis stage fits with some
difficulty into Dujardin's definition of the genus Rhabditis as
its strongyloid origin is indicated, in the male, by a distinct
copulatory bursa supported by chitinous rods, much resem-
bling, though not identical with, that of the parasitic stage.
As, however, Dujardin's definition includes certain species,
the males of which have the " tail provided with membranous
wings," its limits are not much forced, and there is no need to
institute a special term for the free stage of our present species.
As far as can be made out, the commencement of the sexual
differentiation, of the male rhabdites takes place in the last ecdy-
sis, but one preceding that in which completely adult characters
are assumed. At this period, the worm measures about 1/38 inch
in length by about 1/1000 inch at the thickest part of the body,
opposite the still rudimentary sexual gland, which is placed
rather nearer the caudal than oral extremity, the middle of the
fusiform rudiment being about 1/100 inch from the caudal extre-
mity. At this stage the generative gland consists of only one
or two hyaline, multimicleate cells. The copulatory spiculæ
however, are well developed, and do not change to any extent
during the remaining ecdyses. There is, however, 110 sign of
the copulatory bursa, which appears after the next change of
skin, the tail being very long, and tapering so as to form a
sort of flagellimi. Even after the next ecdysis, there is but
little change in the generative gland, which, at this period, con-
sists of a hyaline, fusiform body, containing a few clear nuclei,
* The number of species in which such a life history has been proved
is constantly increasing. Only lately the fact has been made out in the
case of Strongyus striyosus and S. retortæ formis by Prof. A. Railliet,
Bull. Soc. Zool. France, XIV. (1889) page 375-7.
G 2
( 76 )
placed ventrally, and measuring 1/400 inch long by 1/2500 inch in
diameter. The caudal extremity is rather abruptly conical, and
now shows a well-developed copulatory bursa, consisting of a
delicate transparent membrane, shaped like a finger nail, and
projecting laterally a good deal more than it does beyond the
point of the obtusely conical tail. It is supported on either
side by three simple chitinous rods of uniform diameter, which,
taking their origin in the cuticle of the tail, pass from it, outwards
and backwards, quite to the edge of the membrane. The
width of the entire organ barely equals that of the greatest
diameter of the body, and it extends up its sides only 1/500 inch
from the extreme point of the tail. Just above this point, on
either side of the middle line of the body, may be seen the
copulatory spiculæ, consisting of two pointed chitinous rods, of
a deep yellow-brown colour, and about 1/1000 long· Their
bases are placed at some distance apart, but their points, when
retracted, touch, so as to form a V, each being contained
within a separate sheath, the two sheaths, however, joining to
form a common opening, which receives also the mouth of the
duct of the generative gland, and together open into intestine
close to the anus, to form a short cloaca. The form of these
spicules differs greatly from the copulatory organ of the entozoic
stage of the worm, in which it is, proportionally, much longer,
and as it does not greatly exceed it in actual thickness, is a
much slenderer structure. In the entozoic stage, too, the two
spicula are kept in habitual contact, so that they can only be
separated by dissection, appearing to be, in some way, locked
together, and they end in a very minute but distinct hook.
These spicu1æ are protrusible, and may be seen in different spe-
cimens in a variety of positions, and when seen in profile, often
appear like a couple of hooks projecting from the ventral
aspect of the tail. In other respects the worm as yet differs
but little from the younger embryos already described,
almost the entire body cavity being filled by the intestinal
canal, the excretory gland, which forms so prominent an
object in the mature stage, being not yet sufficiently developed
to be easily made out.
When fully developed, the mature male rhabdites measures
1/36 inch 1/24 inch in length, but little exceeding in this matter
the size of the worm during its two preceding changes of skin. It
has, however, become markedly thicker, its greatest diameter,
which is still placed in the same situation, reaching from
1/500 inch — 1/300 inch. The structure of the nutritive organs
remains unchanged, but, lying beneath the ventral aspect of the
( 77 )
intestinal canal, may be seen a glandular body of considerable
relative size, measuring 1/170 inch in length by 1/1000 inch in dìa-
meter. Behind it ends in a blunt rounded extremity, while in
front it tapers off to form a duct. It is lined with an epithe-
lium of very small, nearly spherical, nucleated cells. In one or
two instances I have doubtfully succeeded in tracing the duct of
this gland to near the excretory pore, and have little doubt that
the organ has an excretory function.* It certainly forms 110
part of the generative gland, the anterior end of which it
overlies. On casual examination, it appeared possible that
it might be a doubled-over end of the generative gland, but
more careful focussing showed that this could not be the case.
Were it a reflected position of this organ, the blind end would
contain the least-developed cells, and the latter would become
progressively advanced in development as one proceeded to the
assumed point of reflection, whereas the contrary is the case,
the blind end being filled with well-developed cells, while
near the point where the faintly-seen, duct commences, the
cells become granular and degenerated. It is present in adult
males and females alike, and is especially easily made out
where the animal has been' killed by the cautious addition of
alcohol, just before the protoplasm becomes opaque from the
action of the re-agent. The histological investigation of these
O
O
O
organisms is excessively difficult, as, owing to the resistent
nature of the chitinous cuticle, the internal organs cannot be
acted upon by re-agents sufficiently soon to forestall those
early putrefactive changes which are fatal to the production
of really instructive preparations.
Owing to their small size, it is impossible to slit them,
or make openings, as one would do in the case of larger
organisms, and the method of sectionizing is equally impracti-
cable, as, by the time they have passed through the various stages
of hardening and imbedding, nothing but a chitinous ring
remains. Fortunately, however, their great transparency goes
far to neutralize these disadvantages.
The generative gland, which has now definitely assumed
the characters of a testis, consists of a single tubular body,
commencing a little behind the second pharyngeal bulb.
* While the above was passing through the press the August 1890
number of the "Journal of the Eoyal Microscopical Society" came to hand.
It contains (page 461) a note of a paper by Dr. O. Hamann in the Zool.
Anzieg. XIII. (1890) page 210-2, in which this organ is clearly described ; and
it is stated that there is no doubt about the existence of an external opening,
and that the organ is a lemuisctis homologous with those of the Acantho-
cephala, and therefore, as I surmised, has a probably excretory function.
( 78 )
At its anterior end, it exhibits, in optical section, a double row of
clear, finely granular cells, each possessing a single nucleus and
nucleolus. As one proceeds backwards, these cells become larger,
until, about half way along the length of the body, they attain
so large a size that they can only lie in a single row. The
most anterior examples of these larger cells contain only a
single nucleus, but further back they become multinucleate,
and, by careful focussing of the most developed, a distinct
brood of daughter cells can be made out within them. It
is within these latter that the spermatic elements take their
origin, the whole process being one of endogenous cell multi-
plication. Finally, the large cells burst, and the hindmost
part of the generative duct will, in perfectly mature speci-
mens, be found to be filled with the spermatozoa, which are
small rod-like bodies thicker at one end than the other, and
so tending to the well-known hat-shape so often seen in nema-
todes. They are capable of ameboid movement, but are
destitute of any lash. As the little creature grows older, the
proportion of its length filled with the large single cells increases,
while those arranged in double row diminish, until, at length,
the whole of the anterior portion of the body is filled with
the large mother cells only. This is, of course, owing to the
progressive development of the cells, and to the circumstance
that no new ones are formed to take up the place of those that
have attained complete development. When all its spermo-
genic cells have completed their development and discharged
the spermatozoa to which they have given birth, the rhabdites
die. The copulatory bursa of the fully-grown rhabdites, though
agreeing in general form, differs a good deal in detail from
that of the immature form found before the last change of skin.
In this stage, it will be remembered, there were, on each side, but
three simple supporting ribs. In the adult stage, there are six
ribs on either side, of which, counting from the front, the first,
fourth, and sixth alone reach out to the edge of the membrane.
The second is the shortest, not reaching half its breadth, while the
third is a good deal longer. The fifth attains very nearly to the
edge of the membrane, and has the additional peculiarity of
being bifurcated to about half its length.
I have never succeeded in finding a pair in copula, but
the female is probably grasped in much the same way as in
the entozoic stage. It is generally supposed that, in this
latter stage, the grasping action of the copulatory bursa is
assisted by a viscid secretion, and this view receives support
from the structure of the caudal end of the rhabditis stage, in
( 79 )
which are to be seen a number of cells of unmistakably
glandular character, which may possibly be concerned in the
secretion of some such fluid. These cells are situated absolute-
ly in the point of the tail, and so are quite beyond the end
of alike the intestine and the generative duct.
In the female rhabdites the changes closely follow those
that take place in the male, though they are not so externally
prominent, on account of the absence of the copulatory bursa.
The generative gland is, for a long time, exactly alike in both
sexes, but it makes its appearance nearer the oral end of the
female than in the male, being placed a trifle nearer to it than
to the aboral extremity, but, beyond this, there is nothing to dis-
tinguish it from a male. At a stage corresponding to the
appearance of the copulatory spiculæ in the male, the female
external generative opening makes its appearance. It is a
small oval aperture placed on the ventral aspect of the
body, rather nearer the head than the tail, and is guarded
by a thickened chitinous ring. The number of changes of
skin between the commencement of sexual differentiation, and
maturity appears to be the same in both sexes, but, up to the
last change, the appearance of the internal generative cells is
closely similar ; only, at all stages, the furthest developed
sexual products, instead of being found, as in the male, towards
the caudal end of the animal, are placed opposite the opening
of the duct, near the middle of the body, and grow less and less
mature as one proceeds, on the one hand, towards the tail, and
on the other towards the mouth.
The single ovarian tube, in fact, extends in both directions
from the genital opening, and hence the least developed germs
may always be found in two situations near the head, and the
tail respectively. Instead, however, of developing into the
mother cells of spermatozoa, the germ cells in this case develop
directly, without any process of endogenous multiplication,
into ova. The ova produced by the rhabditic stage are in all
respects exactly similar to those of the entozoic, which have
been already described, and those first extruded are laid in
much the same stage of development as those met with in the
fæces of infected persons, viz., 2-4 segmented. During the
process of laying, the female remains almost motionless, and
does not, I am inclined to think, take any food after the
completion of maturity. As more and more eggs are laid, the
more backward germs, from either extremity of the ovarian tube r
advance towards the middle of the body, and develop, in their
turn, into distinct ova, until at length, owing to the emptiness
( 80 )
of the intestinal canal, she becomes from end to end little
else than a sausage-shaped bag of ova. The development
of these latter, however, proceeds at a somewhat more rapid
rate than the hatching process, so that soon the eggs,
when hatched, already contain living embryos, instead of a
merely segmented yelk. Finally, when the female is becoming
nearly emptied of eggs, they hatch out within her body,
and appear to feed on her organs, only gaining access to the
exterior by the rupture of her body-wall, by decomposition.
Thus, this animal presents the peculiar phenomenon of being
oviparous in her young maturity, and ovoviviparous in her old
age, and, as may be seen, the completion of the process" of
laying necessarily involves her death also. As they do not
appear to require food after attaining maturity, the whole
process can be easily watched in a cell containing water, and I
have followed it throughout in several instances. The num-
ber of eggs produced, is considerable, but is quite insignificant
in comparison with the myriads produced by the entozoic
stage of the creature. The largest number observed to be
laid by any one female after isolation in a watch-glass was 70,
but the necessity of being sure of complete maturity prevented
one's being able to select them at the absolute commencement
of the process, so that, all considered, we shall probably be
not far wrong if we double this figure as a fair average of the
family produced by a single female. As has already been
pointed out, the process of reproduction absolutely necessitates
the death of the female, and her whole life does not much
exceed seven days.
In examining impregnated females, the copulatory spicula
of the male may often be seen sticking in the opening of the
generative duct, so frequently so indeed, that this mutilation of
the male is probably the rule, and, if this be the case, it lends
strong support to the idea that the life of the male is of no
longer duration than that of the female, as, after such a muti-
lation, his functional utility would necessarily cease. The
female is considerably larger than the male, sometimes reach-
ing the length of 1/15 inch and a breadth of 1/200 inch, so that
with strong oblique transmitted light, they can be made out with
the naked eye when once their position has been ascertained
under a lens. The tail of the female is acuminate, a small
sharp process projecting from the otherwise blunt tail. In the
remaining points of her anatomy she exactly resembles the male.
In both sexes, the margin of the lipless mouth is armed with
a circlet of very minute papilke, which, being rather sharp-
( 81 )
pointed, might well be mistaken for teeth. The nervous
system is best studied in large living specimens, which have
been rendered motionless by immersion in water containing
as much thymol as it will take up. I found this re-agent ex-
tremely useful for this purpose, as it stupefies without killing,
and it is quite sufficient to quiet the naturally sluggish adult
rhabdites. It is not, however, sufficiently powerful to stop the
violent motions of younger embryos, for which purpose, about
4 per cent, of absolute alcohol must be added to the mixture.
The structure and position of the central ganglion has
• already been described, but the distribution of the nerve cords
issuing from it remains to be noticed. Several (6 or 8) fibres
proceed forwards, along the sides of the anterior pharyngeal
bulb, to the neighbourhood of the mouth, and on these fibres
are found a number of irregularly disposed ganglion cells,
but little inferior in size to those composing the central
ganglion. On each side, a single chord proceeds backwards,
and these, too, are provided with irregularly disposed ganglia,
but they cannot be traced far, as, owing to the crowding of
parts below the second pharyngeal bulb, they are soon lost
to view, but, in the clearer space near the tail, cells that seern
to have a ganglionic character can again be made out, and
there can be little doubt that these are connected by coinmis-
sural strands with the cesophageal nerve ring.
The embryos hatched out from the eggs of the rhabdites
are identical in size and appearance with those already
described as hatched out from the eggs produced during the
entozoic stage of the worm, and it is entirely a matter of chance
whether they will develop into free organisms like their
parents, or become parasites like their grandparents.
In all probability, the generation immediately produced
from the eggs of the entozoic stage would prove harmless, if
introduced into the human intestinal canal, as the life cycle
would be incomplete, were they to develop into parasitic
nematodes like their parents. There can, however, be no
doubt of the infectiveness of the progeny of the rhabdites, and
it is probably universally by the agency of .these that infection is
effected. Attempts have already been made, by other investi-
gators, to infect sheep, pigs, and other domestic animals, but
without success, so that it was clearly useless to make any
experiments with these, and accordingly the small short-tailed
monkey (Macacus rhesus]., very common in Assam, was selected
as a subject for experimentation, but, as will be seen, only
partial success has been met with. The first experiment con-