PET 
originally mineral ones, and drawn up out of the earth 
into the vefiels of the plant. 
It is remarkable, that all the petroleum got from the 
lake of Mount Chiaro in Italy is white, whereas that of 
Modena is yellow, and that of Parma brown. Thefe 
wells or holes continue to furnifti the oil in different 
quantities for a confiderable time ; and, when they yield 
no more, they pierce the dates in fome other place. 
Petroleum, when fhaken, yields a few bubbles 5 but 
they fooner fubfide than in almoft any other liquor, and 
the liquor refumes its clear date again almoft immediately. 
This feems owing to the air in this fluid being very 
equally diftributed in all its parts, and the liquor being 
compofed of particles very evenly and nicely arranged. 
The extenfibility of this oil is alfo amazing. A drop of it 
will fpread over feveral feet of water, and in this condi¬ 
tion it gives a great variety of colours ; that is, the feve¬ 
ral parts of which this thin film is compofed a£l as fo many 
prifms. 
The moft fevere froft never congeals petroleum into 
Icej and paper wetted with it becomes tranfparent, as 
when wetted with oil 5 but it does not continue fo, the 
paper becoming opaque again in a few minutes, as the 
oil dries away. 
Spirit of wine, which is the great diffolvent of fulphur, 
has no effedt upon petroleum, not even with ever fo long 
a digeftion. It will not take fire with the dephlegmated 
acid fpirits, as oil of cloves and other of the vegetable 
efl'ential oils do: and in diftillation, either by balneum 
mariae or in fand, it will neither yield phlegm nor acid 
fpirit; but the oil itfelf rifes in its own form, leaving in 
the retort only a little matter, thick as honey, and of a 
brownifh colour. Whoever, therefore, would ufe this oil 
in medicine, muft take it as nature has prepared it, art 
having no power to make any alteration in it. Mem. Acad. 
Paris, 1715, 1736. 
PETROLEUM CREE'K.orEAR'TH-OiL Creek, called 
by the natives Yaynangheoum , a town of the Birman em¬ 
pire, on the Irawaddy, receives its name from the wells 
of petroleum about five miles to the eaft of it, which fup- 
ply the whole empire, and many parts of India, with this 
ufeful produdh The mouth of the creek, when captain 
Symes viiited it, was crowded with large boats, waiting to 
receive a lading of oil; and immenfe pyramids of earthen 
jars were raifed within and round the village, difpofed in 
the fame manner as (hot and (hells are piled in an arfenal. 
This place is inhabited only by potters, who carry on an 
extenfive manufa&ory : the fmell of the oil is dated to 
have been extremely offenfive. Of the wells in this dif- 
tritt there arefaid to be 520, which yield, annually, more 
than 400,000 hogflieadsof petroleum. Symes's Ava, vol. ii. 
PETROMY'ZON, /. the Lamprey ; a genus of fifties 
of the order chondropterygii. The name is originally 
Greek, derived from Trelpov a ftone, and to fuck ; this 
fifti being ufually found in rivers, adhering to the (tones 
by fucking, and fo keeping its place. The Latin name, 
lampetra, imports the fame thing. Generic chara&ers— 
Head flenderer than the body 5 mouth longer above 
than beneath ; teeth orange-coloured, hollow within, and 
in double rows; feven fpiracles on each fide the neck; 
on the nape a fiftulous opening; neither pectoral nor 
ventral fins. 
According to the laft edition of Gmelin, there are only 
fourfpecies, but Cepede enumerates nine : we (hall notice 
them all, taking firft thofe referred to by Gmelin. They 
all adhere to rocks, and other bodies by the mouth, the 
edges of which are jagged. The body is eel-(haped, 
flippery, and mucous ; they live a long time out of the 
water, and feed on worms, infe&s, fmallerfifti, and dead 
bodies; the belly is long, and narrow ; the vent is near 
the pinnate tail. They have two dorfal fins; round the 
eyes are numerous perforations; the tongue is femilunar 
and hard ; the teeth ferrate. They are (o tenacious of 
life, that they will keep their hold on a folid fubftance 
even after part of their body is cut away; and will live 
PET II 
in that mutilated (late for feveral hours in the water. 
Their food is worms, infers, fmall fi(h, and (lime or mud. 
They are defcribed in the following modern fyftematic 
works: Gmelin’s Linn. 1513. Turton’s, 931. Cepede, 
i. 3. iv. 665. Shaw’s Gen. Zoology, v. 251. Bloch, i. xii. 
1. Petroinyzon marinus, the fea-lamprey: mouth 
papillous within ; fecond dorfal fin diftin 61 from the tail. 
In its general appearance, this fi(h makes a near approach 
to the eel-tribe, and particularly to the Murtena genus ; 
which fee. It arrives at a confiderable fize, and to the 
length of more than three feet: the generality of the 
Britifti fpecimens, however, are not fo large. The ufual 
colour of the lamprey is a dull-browni(h olive, clouded 
with yellowi(h-white variegations ; the back, as in molt 
fifties, is darker than the other parts, and the abdomen 
paler; the fins are tinged with dull orange, and the tail 
with blue; the eyes are rather fmall; the mouth large, 
oval, fituated beneath, deeply concave, and lined or paved, 
as it were, with feveral circular rows of (harp, triangular, 
orange-coloured teeth; the tongue, which is (hort and 
crefcent-ftiaped, is alfo furnifhed with a row of very fmall 
teeth round its edge. On the top of the head is a fmall 
orifice or fpout-hole, through which is difcharged the 
fuperfluous water taken in at the mouth and gills. Near 
each eye are two rows of much fmaller foramina, one row 
confiding of five, and the other of fix; thefe are fuppofed 
to be the orifices of the glands which fecrete the vifcid 
moifture neceflary for lubricating the (kin ; on each fide 
the neck, commencing at a fmall diftance beyond the 
eyes, is a row of feven pretty large, equidiftant, round 
fpiracles or breathing-holes, each leading to a deep fac- 
culus, lying in an oblique direftion towards the head: 
thefe feven facculi on each fide are lined with a red 
plaited membrane, and have no communication with each 
other, but pafs by their refpe&ive double dufts to the 
infide of the mouth. Towards the lower part of the back 
commences the firft dorfal fin, which is rather (hallow, 
with a rounded outline; the fecond, which commences 
at a very fmall diftance from it, is nearly of the fame ex¬ 
tent, but with a fubtriangular outline ; the tail is (hort, 
and (lightly rounded. 
The lamprey is an inhabitant of the ocean, afcending 
rivers chiefly during the latter end of winter and the 
early months of fpring; and after a refidence of a few 
months in fre(h water, again returns to the fea : it is vi¬ 
viparous, and the young are obferved to be flow of growth ; 
contrary to the aflertions of fome writers, who have fup¬ 
pofed the lamprey to be a (hort-lived fifli. When in mo¬ 
tion, this fifti is obferved to fwim with confiderable 
vigour and rapidity, but it is more commonly feen at¬ 
tached by the mouth to fome large ftone or other fubftance, 
the body hanging at reft, or obeying the motion of the 
current: fo (trong is the power of adhefion exerted by 
this animal, that a ftone of the weight of more than twelve 
pounds may be raifed without forcing the fifh to forego 
its hold. The general habits of the lamprey feem pretty 
much to refemble thofe of the eel, and it is fuppofed to 
live principally on worms and young fi(h. Like the eel 
it is remarkably tenacious of life; the feveral parts, when 
cut in pieces, will long continue to move ; and the head 
will ftrongly attach itlelf, for feveral hours, to a ftone, 
though by far the greater part of the body be cut away 
from it. This amazing power of fuftion muft arife from 
the animal’s exhaufting the air within its body by the 
hole over the nofe; while the mouth is clofely fixed to 
the objeft, and permits no air to enter. The weight 
which the lamprey is by this means able to fuftain, will 
be equal to that of a column of air of the fame circumfe¬ 
rence with the animal’s mouth. 
The lamprey is found in the North Sea, whence in the 
fpring it pafles into the Elbe, the Havel, and the Saale, 
which run into it; at certain feafons, it is found in many 
of the Britifti rivers, and in the Irilh; alfo in France, 
Italy, and America, where they grow about three feet 
long. They are found likewife, though not plentifully. 
