NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
6
spur-like process. All segments have a few short spines. There is a terminal
papilla bearing a few short spines.
The eyes are absent.*
The mouth is situated upon the inferior surface of a papilla. The papilla
carries six short curved spines arranged in a circlet. A second circle of similar
but larger spines surrounds the papilla at a short distance.
At each of the posterior angles of the head, there is a large flat chitinous
expansion, from which arises a single, very long, stout hair, and one or two small
spines. The hair passes back as far as the abdomen. On the ventral surface
of the head there are two medium sized spines arising near the base of the antenna.
The thorax is small. It is separated from the abdomen by a constriction.
The posterior angles of the chief dorsal plate are thickened and carry a number
of stout spines. Internally to the spines, a long hair resembling that on the
head, passes backwards as far as the first segments of the abdomen. Ventrally
there is a narrow sternal plate, on either side of which the coxæ of the three
pairs of legs arise.
The legs consist of four large segments.
The proximal joints of the legs (coxæ) are oval and of large size. They
bear on their anterior surface, especially at their distal extremities, some small
spines. The second joints are small. They carry small spines anteriorly. The
third joints are large and globose. They are armed with spines on their anterior
surfaces. The fourth joint is large and triangular. It is smallest in the first
pair of legs, and very large and massive in the third pair. The apex of the
triangle articulates with the third joint. The anterior angle of the base is con-
tinued as a strong curved claw. The posterior angle forms a pad. Between the
two is a hollow in which the shaft of the host's hair is held. The claw is jointed
at its base. A second articulation is visible a short distance above this. The
claws increase in size and massiveness from before backwards. That of the third
legs is an extremely large mass of chitin shaped like a parrot's beak.
The abdomen consists of nine visible segments. The differentiation of the
ninth segment is more readily made out in the female than in the male. Each of
the first six segments carries on its posterior border, both ventrally and dorsally, a
fringe of hairs. The seventh segment carries only two hairs on the dorsal surface.
Laterally the segments carry long stout hairs, as well as short powerful spines.
In the adult, the first segment carries a single hair. The 2nd, 3rd, 4th, 5th, 6th,
7th and 8th, each two hairs, of which those of the 2nd and 6th segments are the
longest. The eighth segment in the male, carries a short hair laterally. In the
female it carries a number of stout spine-like hairs. The ninth segment has, in
the female, a slit-like opening guarded by two chitinous plates. In the male, a
* NOTE.— Gerbillus indicus is nocturnal in its habits and an extensive burrower .
7
horny papilla bears a circlet of short curved spines. On the dorsal surface of
the papilla there is a large opening. In the male the penis forms a conspicuous
object. It terminates in a horn-shaped process.
The ova measure .48 m. m. in length. They are fixed to the hair
about half way up the shaft. The attached end lies towards the base of the hair.
The young escape from the egg as forms closely resembling the adult.
The abdomen, however, is very small and the hairs projecting from it propor-
tionately very long. In the immature forms the abdominal segments carry a
fringe of only four hairs instead of many as in the adult.
St ructure.
The alimentary canal. —The alimentary canal consists of the following
portions :—
F o r e - g u t
.
.
.
Mouth.
Chitinous pharyngeal pump.
Oesophagus.
Mid-gut
.
.
.
1st portion or descending part of mid-gut.
2nd portion or ascending part of mid-gut.
Pyloric ampulla with the origin of malpighian tubules.
H i n d - g u t .
.
.
Intestine.
Rectum.
The mouth is very small. The opening is situated beneath the prow-like
anterior portion of the head.
The pharyngeal pump is long and narrow. It passes through the head
and into the thorax. It ends in the front part of the thorax in a number of
chitinous bars.
The oesophagus passes backwards and upwards, surrounded by the large
ganglionic masses. It is a delicate wrinkled tube much folded upon itself. It
enters the large massive mid-gut with no appreciable proventricular fold.
The mid-gut is sharply bent upon itself, so that it forms a U shaped organ.
The first portion is the largest and its walls are thickest. It is lined by large
granular cells with large nuclei. In the distended organ the cells are flattened.
In the empty viscus they are cubical. Externally there are longitudinal and
circular fibres, arranged to form an open network. During life rythmical contrac-
tions are constantly taking place. The contents are blood, either unaltered in
appearance, or partially digested. The mid-gut, especially the more massive
first portion, occupies, when distended, most of the abdominal space not taken
up by the ovaries.
8
The pyloric ampulla* is a dilated portion of the mid-gut and is supplied with
numerous circular muscles. Into it open four malpighian tubules. These enter
two on each side, close together. Immediately beyond the malpighian tubules,
a distinct dividing line between the mid-gut and the intestinal epithelum is seen.
The intestine is straight and thin-walled. There is no differentiation into
large and small intestine. It passes from the muscular pyloric mass, close
beneath the abdominal terga, to the rectum. The cells lining the cavity are
small. It has a layer of circular muscle fibres, and outside this a number of
longitudinal fibres. The nuclei of the latter form conspicuous objects in the
fresh tissues.
The rectum consists of a distended globular portion, containing rectal
papillæ, and a straight narrow portion leading directly to the anus at the apex
of the ninth segment.
The salivary glands. —These are small oval structures, consisting of a
single acinus, which rests upon the anterior portion of the mid-gut in the first
abdominal segment. A duct, of delicate structure, leads forwards towards the
pharyngeal pump. Each acinus consists of several large cells with a central
clear very refractile space.
The malpighian tubules. —These resemble the tubules of insects generally
and consist of cells with large oval nuclei. The cells are much drawn out and
nuclei are situated at considerable intervals along the tube.
The generative organs. —The female organs consist of an ovary on each
side opening into a short common oviduct. Each ovary is composed of five or
six follicular tubes, each of which is attached to the body wall by a delicate apical
strand of tissue, and opens into the oviduct of its own side. Each contains two
or more egg follicles in different stages of development. In the adult louse
two fully matured fellicles, one lying on each side, occupy the greater part of
the abdomen. All follicles, except the youngest, consist of a single layer of
cubical or columnar cells surrounding an ovum and nurse cells. In the mature
follicles the nurse cells which lie towards the apex of the follicle have become
absorbed.
The spermatheca. —This is a large thin-walled chitinous sac, opening by a
short tube near the anus. It may be empty or may contain masses of sper-
matozoa.
The male organs. —The testes are curious double peg-top shaped organs.
Each opens by a narrow tube into a wide seminal vescicle, in which masses of
spermatozoa are seen. The duct of the testes opens at a distance from the end
of the seminal vescicle, so that this possesses a caecal extremity. The seminal
* NOT E.—A similar dilated portion of the alimentary canal is present in the mosquito. In the mosquito
the dilatation is derived from the hind-gut ; in the louse it appears to be derived from the mid-gut.
9
vescicles lie across the abdomen, and open together into a short straight tube
surrounded with large muscle fibres. This tube in turn passes into the penis.
The fat body.—The fat body is well developed. In the head and thorax it
forms pads lying between the muscles and the organs. A very conspicuous pad lies
beneath the pharynx, and other masses are situated close to the salivary glands.
In the abdomen, the fat body consists of a number of conical masses attached
by their apices to the body wall, near the origin of the lateral hairs. The bases
of the conical masses lie against the mid-gut and other viscera to which they give
support. The cells which compose the fat body contain, as well as oil globules,
masses of opaque granules apparently of a calcareous nature.
In addition to the fat body, certain very curious cells are seen free in the
body cavity. On dissecting the abdomen, these are liberated and lie about on
the slide, quite unconnected with the other tissues. They are oval or spindle
shaped, measuring 140µin length. At one or both poles they have a delicate
spike-like process. They contain two nuclei and possess a fairly resistant
cuticle, which is left as a shrunken structure when the cell contents have been
extruded. In spite of the parasitic-like aspect of these cells, they appear to be
normal tissue cells of the louse. Somewhat similar cells, though in less
numbers, were found when dissecting a species of louse infesting calves.
Certain groups of small, partially free, cells are also seen in the body cavity,
especially near the terminal segments. The nature of these and of the large cells
noted above is not clear.
The muscular system. —Powerful muscles are connected with the pumping
organ and the large antennæ. They occupy much of the space in the head,
not taken up by the large ganglia. The thorax is mainly muscular. The
abdomen has certain small dorso-ventral muscle bundles, which when seen in
optical section in the fresh louse are conspicuous refractile bodies. A band of
muscle passes along each side of the body, and is attached to each segment
near the origin of the long hairs. In the male, powerful muscles are seen in
connection with the penis.
The tracheal system. —Two large spiracles of oval shape are situated just
behind the spiny area of the thorax. From these, and smaller abdominal stig-
mata, tracheæ form loops with distributory branches for the tissues. The
tracheæ are not very large or numerous.
The nervous system. —The ganglionic masses of the head are of great size.
The thoracic ganglion is also a large and conspicuous object, especially in sections.
The circulatory system. —There is a pulsating chamber beneath the 6th
and 7th abdominal terga, from which a dorsal vessel, also pulsatile, passes for-
wards over the mid-gut. Muscle fibres of a peculiar nature pass outwards from
the chamber to the body wall.
C
10
Development of the parasite in the body of the louse.
In order that feeding experiments might shew unequivocal results, a young
animal was selected in whose blood parasites were extremely abundant. As a
cursory examination of the fur revealed no lice, a number were transferred from
four older animals. They quickly disappeared among the hairs.
On the fourth day ova were noticed on the fur about the head. Two lice,
presumably belonging to those placed on the rat, were removed for dissection.
One was dissected immediately after removal, the other was left overnight in a
moist chamber.
Dissection of the first louse shewed very numerous free vermicules in the
mid-gut and intestine. A number were also scattered about the preparation, but
may have been derived from the gut as this was ruptured. The vermicules
exhibited active movements, mainly of lateral flexion. Very few encysted
parasites were present.
No forms were seen in the salivary glands or ovaries.
A dry preparation was made from the mid-gut and its contents and stained
with Romanowski's stain. Numerous large vermicule forms, in various attitudes,
were seen among altered blood corpuscles. As many as a dozen vermicules
were to be seen in single fields of the microscope. Compared with stained
specimens of free vermicules from the peripheral blood of the rat, these forms
appeared larger and finer. The chromatin masses, especially, were noted as
extending through a greater portion of the parasite. The protoplasm of the
vermicules was, in almost every case, free from granules and stained a clear
blue. Some of the vermicules had assumed a characteristic crescentic form
(Fig. 9.)
Dissection of the second louse shewed many free vermicules collected in
the pyloric ampulla (fig. 11). A motionless vermicule, which had become
crescentic in shape, was detected in the body cavity in the neighbourhood of the
rectum. In this dissection the alimentary canal was apparently free from
injury. The vermicules in the gut shewed sluggish movements chiefly of
lateral flexion. Only a single, still unchanged, encysted form was noted.
On the seventh day the rat was killed and the lice collected. Many
young lice, apparently just hatched, were observed. Dissection of several of
these shewed many very active vermicules in the gut. In the dissection of
the larger specimens, made on this day, certain very striking large cysts
undoubtedly of parasitic origin, lying free in the body cavity of the louse
were found. The most developed cysts were of large size, measuring
as much as 350μ in diameter, and being readily seen under a low power
lying in the abdomen of the infected louse (fig. 20). They were most often
seen in the anterior portion of the abdomen, but were present also in other
11
parts. On pulling apart the abdominal segments, they readily became free
upon the slide, and were easily visible to the naked eye, as minute white spheres.
Under the microscope, the large cysts were seen to be filled with a number of
small oval cysts. Each of these again contained six to eight crescentic bodies
lying as a rule slightly obliquely in the long diameter of the cyst. On the rup-
ture of the smaller cysts, the crescentic bodies were liberated, and were seen
to be sausage-shaped bodies with blunt extremities, measuring 15µ in length
and 4µ in thickness. A refractile area (nucleus) was situated nearer one
extremity than the other. The protoplasm was granular, but in both extre-
mities clear areas resembling vacuoles were conspicuous. No movement
was observed in the bodies. On rupture, the wall of the small cysts became
folded so as to form elongated spindles of very regular pattern. In the empty
cyst a small granular mass (reliquat) was visible. (Figs. 15 and 16.)
Younger stages of the large cysts were readily made out. All appeared
quite free in the body cavity. The smallest cysts seen measured 10 µ in diameter.
They shewed a double contour, and a central clear refractile spot. Later
stages are proportionately larger. In medium sized cysts a thick clear outer
zone is present within the double contour of the cyst wall. The contents are
granular, the granules sometimes being arranged in clusters. As maturation
advances, the central granular portion becomes more opaque. At this stage
the parasite has a characteristic aspect so that it can be detected, even
without dissection, lying in the abdomen of the louse. The central granular
mass is usually situated slightly excentrically, so that the clear zone is thicker
at one side of the cyst than at the other. Before full maturation, the central
mass becomes divided into oval bodies containing granular protoplasm arranged
in a characteristic manner (fig. 17). Attempts to obtain satisfactorily stained
specimens of the immature stages were not successful. (Figs. 12, 13
and 14.)
In stained films made from the ruptured mature cysts, beautiful specimens
of the liberated sausage-shaped bodies were seen, but the collapsed and
unruptured cysts remained unstained. Considerably nearer one extremity than
the other, so that it divides the protoplasm in two unequal halves, there is a large
granular densely staining chromatin mass, and the body of the parasite
at this point shews a marked constriction. The protoplasm is granular but
contains in either extremity a conspicuous clear area.
In all except two of eleven lice removed from the rat, cysts in some stage
or other of development were found by dissection. In one louse three fully
mature cysts, two medium sized cysts and three small cysts were found.
In none of the lice was any unusual appearance observed in the salivary
glands or ovaries.
C 2
12
In addition to eleven lice which were dissected in the fresh condition, two
were fixed in alcohol and reserved for the preparation of sections. Sections cu
in paraffin were stained with hæmatein.
In one instance the mid-gut was found fully distended with recently drawn
blood, the corpuscles of which were scarcely altered in appearance. Numerous
vermicule forms were seen. They were especially abundant near the walls of the
gut. One or two examples only were seen of forms still encysted in corpuscles.
The vermicules were usually stretched out, so that they gave a vivid impression
that they were travelling through the mass of closely packed red cells.
In the body cavity of the louse a large cyst was noted, lying between the wall
of the mid-gut and the 5th and 6th abdominal terga. It contained numerous
darkly stained bodies, showing a central clear area and a nucleus. These bodies
appeared to be the immature stages of the contained cysts, prior to the formation
of the sickles. In the second specimen, the mid-gut was empty. No vermicules
were seen in the lumen. A single vermiculu was detected in the upper part of the
intestine. The abdomen was distended with nearly mature ova. No unusual
bodies were seen in these, nor in the salivary glands. No cysts could be detected
in the sections.
The appearances to be expected, being now familiar, further dissections
were made, A rat which had been placed in a separate cage, on account of
the presence of numerous parasites in the blood, was noticed to have a few lice
and a considerable number of ova on the hairs about the head. Three lice were
removed and dissected with the following result :—
Louse
.
. . 1 Nil.
"
. . . 2 One medium sized cyst.
"
. . . 3 Two medium sized cysts
and one small cyst.
The rat was kept under observation for five days and then killed. Ten
lice were dissected with the following result. : —
Louse
.
. . 1 Nil.
" .
. . 2 Nil.
" , , .
.
. 3 One medium sized cyst.
" , .
. . . 4 Two fully matured cysts.
" .
. . 5 Two medium sized cysts.
" .
. . 6 Nil.
" .
.
. 7 One, fully matured cyst.
" .
.
. 8 Nil.
"
.
.
. 9 Nil.
"
.
.
. 1 0 Two large and one medium sized cysts.
A rat with a scanty infection was killed and the lice collected. Dissection
of seven lice gave the following result :—
Louse
. . . 1 N i l .
"
. . . 2 Nil.
13
Louse
.
.
. 3 One half grown cyst.
"
.
.
. 4 Nil.
"
.
.
. 5 Nil.
"
.
.
. 6 Nil.
"
.
.
. 7 Nil.
A rat in whose blood I had never found more than an occasional parasite,
was found to be harbouring a certain number of lice. Nine adult lice only
were obtained. No cyst was found in any of these.*
Behaviour of crescentic bodies when treated with intestinal juice.—A
number of rats, which were kept together in a large cage, were found to have
become almost free from lice in a comparatively short time. Several rats from
the same batch, which had been placed in separate cages were, on the contrary,
badly infested. It was thought possible that the animals might clean each
other, especially as they were observed to snap up mosquitoes on the wing and
to eat ants on the floor of their cages. The action of intestinal juice upon the
sausage-shaped bodies was, therefore, tried. A louse, in which two mature cysts
had been detected by low power examination, was carefully broken up in salt
solution. The two cysts were obtained uninjured upon the slide. One was
removed for a separate experiment. A rat was killed and the intestine opened
a short distance below the duodenum.
A small quantity of intestinal fluid was placed upon the cyst, and the whole
covered with a coverglass. Under a low power the large cyst was seen to have
ruptured, and the small contained cysts to be scattered in the intestinal fluid.
A small number of the latter had also ruptured, and the contained bodies were
liberated. The exposed crescentic bodies exhibited some sluggish movements.
The bodies in the cysts remained unchanged. The preparation was placed
in the incubator and examined at the end of an hour. Most of the free bodies
were motionless, and some appeared to have undergone dissolution. The
coverglass was pressed, in order to rupture more of the cysts, and the
preparation placed again in the incubator at 37ºc. At the end of an hour no
changes were seen, and the bodies exhibited no movement. After twelve hours
most of the free forms had disappeared.
Behaviour of the bodies in plasma.—Upon the other cyst, a drop of blood
from the heart of the rat was placed, and the whole covered by a coverglass.
The pressure of the glass ruptured the outer cyst but only a small number of
the contained cysts were ruptured. After a very few minutes, a commotion
was observed among some corpuscles, and a vermicule-like body was seen to
be moving these about vigorously. Other bodies exhibiting active movements
* NOTE.—Since writing the above I have dissected lice from a considerable number of rats. Those
from rats with numerous parasites in the blood consistently shew the cystic bodies, whereas lice from rats
with very scanty or no infection are negative or contain the bodies in very small number only.