34T 
HE.LMIN 
canals take their origin, which pafs along the neck and 
body in parallel lines ; but towards the extremity 
they become fo pellucid and evanefcent, in the more 
minute fpecies, as to efcape the microfcop'e. Its prin¬ 
cipal difference from other taenhe, confifits in its mem¬ 
branous veficular expanfion, which externally appears 
to conftitute its whole form, and in which the head is 
generally concealed. It differs alfo in its habitation; 
for it is never found in the inteftines, but on the furface 
of the vifcera, on the membranes, and fometimes enve¬ 
loped in the fat. In every other refpeCt they are the 
fame ; yet it is not furprifing that its nature has fo long 
been overlooked, fince it is foinetimes diffitn 11 to difco- 
ver the head, often the only organic part of its fyftem. 
Dr. Tyfon fir'ft difcovered hydatids in the livers of 
Iheep ; Bartholine obferved them in the livers-of goats, 
and Pyerus in hogs. To Pallas, however, -we are in¬ 
debted for the firft correct and connected^ account of 
thefe animals, which he has defcribed and figured in his 
Mifcellanea Zoologica. After his publication, Goeze, 
Batfch, Bloch, and others, have added confiderably to 
the flock of information. They found that hydatids 
are, imge'neral, fuperficiai ; that is, fome portion is en¬ 
veloped in the fubftance of the liver, for inftance, and a 
part rifes above it. Yet this is not an univerfal rule ; 
for, as they are very numerous, fome of them muft be 
wholly concealed. Thofe which burrow in the fat are 
entirely covered, and can - never change their place. 
Their lize differs according to their age, and the tempe¬ 
rament of the animal at whofe expence they live. Pal¬ 
las fpeaks of fome as large as the fift, and others (till 
more bulky. Their figure is infinitely varied, but ge¬ 
nerally approaches that of a flatted fphere. Their 
colour is generally yellowilh white, or femitranfpa- 
rent, fometimes flightly red, or of an amber colour ; 
their fubftance is compofed of different membranes, con- 
glutinated, and formed of circular fibres, vifible by 
means of a lens ; but in many animals,- particularly in 
Iheep, they are fufceptible of an evident contractile 
power. Internally, on the part oppofite to the head, 
we'obferve a difc, fomewhat thicker than the mem¬ 
brane, with often a number of fatty tubercles, which 
are fuppofed to be eggs. They are filled, though not 
wholly, with lymph, ufually tranfparent, of an oily 
fait tafte, which becomes cloudy by heat. Thefe vefi- 
cles are obferved to have a motion oi their own, which 
may be ftyled periftaltic, and is often very lively. The 
head is not always at the termination, but often conceal¬ 
ed by the reduplication of its: membrane or Ikin; and 
from this part the hydatid aCts on the vifcus in which 
it lives, and fucks its lymph. The animal is belt ex¬ 
amined by feparating the veficle, and placing it between 
two pieces of glafs, taking care that they prefs very 
gently on the anterior part. The head, in that cafe, 
preffed forward by the lymph, projects ; and with a lens 
the fuckers and humuli are obfervable. 
Hydatids, in the human race, are found chiefly in the 
liver, the fpleen, the uterus, the ovaria, the kidneys, 
the placenta, the lungs, and even the mufcles. Thofe 
in the accumulated fluid of dropfies are fuppofed to be 
the caufe of the difeafe ; and thofe in the' cerebrum are 
laid to attack the brain, and occafion infanity. In the 
human vifcera they occafion acute pains, either con¬ 
tinual or temporary. Their prefence may, it is faid, be 
jfufpeCted by weaknefs, emaciation, and oppreflioifat 
the ftomach ; but thefe fymptoms are owing to many 
other caufes ; and, were theexiftence of hydatids aicer- 
tained, there is, perhaps, no remedy yet afcertained that 
would reach them. Hydatids of the liver are often 
found ina cyftof cartilaginous firmnefs, compofed of 
different Ja'minae, and thicker in fome inftances than 
others. The laminae are white, and apparently lined 
with coaguiable lymph. A cyft often contains various 
hydatids, fome floating loofely in the fluid, and fome at¬ 
tached to its fides ; and alfo of very different fizes, from 
THOLOGY. 
a pin’s head to that of a walnut. The largeft are gene¬ 
rally found floating in the cavity of the abdomen, when 
diftended by dropfy. 
In the inferior animals they appear to be more com¬ 
mon than in'man. They are found in the livers of hares, 
efpedally.thofe which feed in marfliy ground. In rats 
they are very numerous; and in Iheep they occafion the 
vertigo or' flaggers when on the brain, and the rot when 
they bufrow in the liver. In the hog they produce the 
appearance foinetimes called meafles ; and they are 
found alfo in the rein-deer, the goat, and the ox. The 
hydatids of hogs are fometimes found in the fubftance 
of the fat, and in the mjufcles ; but they are moft com¬ 
monly lodged' under the tongue ; and, from infpeCtion 
of that part, the probability of their exiftehce in the 
fle/h may be afcertained. 
The hydatids of man are reducible into the three follow¬ 
ing varieties : i. Th tvifceral hydatid ; its veficle is round 
anteriorly, and pointed pofferiorly ; it is found in the li¬ 
ver, the fpleen, the uterus, and the hydropic facs, of the 
human race ; and is probably a more frequent caufe of 
dropfy than pathologifts have fufpebted ; and there is 
no doubt, ffiould the fadt-prove fo, but that the free 
ufe of ardent fpirit will greatly promote the growth and 
increafeof the hydatids, and confequently of the diforder. 
Their veficles are often lined with an opaque pulpy 
coat, but are more ufually tranfparent. When in the 
ovaria, their moft frequent refidence, they are faid fome¬ 
times to occafion a falfe pregnancy. 2. The cellular hy¬ 
datid is contained in a cartilaginous veficle, grows very 
large, and is found in the integuments of the mufcles 
of the human race, fimilar to that which infefts hogs. 
3. The cerebral hydatid, found on the brain. 
A remarkable cafe of fatality, occafioned by vifceral 
hydatids, is given by Dr.-J. Hunter, as follows : “ A 
man, forty-fix years old, died fuddenly, after fome com¬ 
plaints of pain and difficulty in palling his urine. On 
diffection, the bladder was found to be enormoufiy dif¬ 
tended, and a large tumour filling the pelvis was difco¬ 
vered between the neck of the bladder and the reftum. 
This contained much water, and many hydatids of va¬ 
rious fizes, fronvone inch and half in diameter to the' 
fize of a pin’s head. Other fmaller tumours, contain¬ 
ing hydatids, lay near the heck of the bladder. A large 
tumour was alfo found between the llomach, fpleen, 
and pancreas, and adhering to all three. It was made 
up of fmaller tumours, the contents of which were vari¬ 
ous ; hydatids of different fizes, whole and-burff, matter’ 
like foftened ifinglals, and clear water, with minute 
grains. They had all thick coats, double, and endow¬ 
ed with'a ftrong elaftic power. A\1 the hydatids had 
alfo two tranfparent contractile coats. Some had fmall 
hydatids on their inner furface ; and the grains in the 
water above-mentioned alfo appeared by the microfcope 
to be minute hydatids. 
“Thefe hydatids, in their growth and decay, appear 
to pafs through various ftages ; they are firft found 
floating in the fluid that fills the large hydatid, and'af¬ 
terwards attached to itscpats. The hydatid thus preg¬ 
nant with young, if the expreflion may be allowed, ad¬ 
heres to the neighbouring parts, incfeafes in fize, and 
becomes itfelf a lac, -containing^ numerous fmall hyda- 
Jtids. Thefe after a certain time decay, and the Ikins or 
empty bags are fqueezed together into a fubftance like 
ifinglafs. It is probable that they ftill undergo a fur¬ 
ther change ; two fmall bodies, of the fize of the com¬ 
mon bean, of a cheefe-like confidence; and covered with 
a Ikin, were taken notice of adhering to the bladder near 
its neck; it may be a queftion whether thofe were.not 
the remains of hydatids? but that muft be determined 
by future obfervations. It is to be obferved, that the 
young hydatids are found in two very different ftages j 
in the one they are attached to the coats of a hydatid 
that floats loofe in the parent bag or lac ; in the other, . 
extremely fmall globules adhere flightly to the inner 
