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S E M 
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ven orders of bodies, and under those ten' 
genera. The selenita: of the first order are 
those composed of horizontal plates, and ap- 
proaching to a rhomboidal form : of the se- 
cond are those composed of horizontal plates, 
arranged into a columnar and angular form : 
of the third are those whose li laments are 
scarce visibly arranged into plates, but which, 
in the whole masses, appear rather of a stri- 
ated than of a tubulated structure: of the 
fourth are those: which are fiat, but of no de- 
terminately angular figure: of the fifth are 
those formed of plates perpendicularly ar- 
ranged: of the sixth are those formed of 
congeries pf plates, arranged into the figure 
of a star; and of the seventh are those of a 
Complex and indeterminate figure. 
The structure of the selenitic of all the ge- 
nera of the first order is exactly alike ; they 
are all composed of a great number of broad 
flakes or plates, in a great measure externally 
resembling the Hakes of the foliaceous talcs: 
these are of the length and breadth of the 
whole mass; the top and bottom being each 
onlv one such plate, and those between them, 
in like manner, each complete and single; and 
the body may always be easily and evenly 
split, according to tiie direction ot these 
Hakes. These differ, however, extremely 
from the talcs ; for they are each composed 
of a number of parallel threads or filaments, 
which are usually disposed parallel to the 
sides of the body, though sometimes paral- 
lel to its ends. In many of the species they 
are also divided by parallel lines, placed at a 
considerable distance from each other, and 
the plates in splitting often break at these 
lines; add to this, that they are not elastic, 
and that they readily calcine. The structure 
of those of the second is the same with that of 
the first: but that in many of the specimens 
of them, the filaments of which the plates are 
composed run in two directions, and meet in 
an obtuse angle; and in the middle there is 
generally seen in this case a straight line run- 
ning the whole length of the column; and 
Small parcels of clay insinuating themselves 
into this crack, represent in it the figure of an 
ear of grass so naturally, as to have deceived 
many into a belief that there was really an 
ear of grass there. The other orders con 
sisting only of single genera, the structure of 
each is explained under the generical name. 
See Plate Nat. Hist. fig. 359. 
SELEUCIDiE, in chronology: sera of the 
Seleiioida:, or the Syro-Macedonian a’ra, is a 
computation of time, commencing from the 
establishment of the Seleucidac, a race of 
Greek kings, who reigned as successors of 
Alexander the Great, in Syria, as the Ptole- 
mies did in Egypt. This air a we find ex- 
pressed in the book of Maccabees, and on a 
great number of Greek medals, struck by the 
cities of Syria, &c. The rabbins call it the 
a:ra of contracts ; and the Arabs therik dil- 
karnain, that is, the icra of the two horns. 
According to the best accounts, the first year 
of this xra falls in the year 3 1 L before Christ, 
being twelve years after Alexander’s death. 
SELF-HEAL, the prunella vulgaris of 
Linnaeus. The stem is erect, and about eight 
or ten inches high. The leaves grow on loot- 
stalks, are ovato-oblong, slightly indented, and 
somewhat hairy. The bracteae are heart-shap- 
ed, opposite, and fringed. The flowers are w hite 
or purplish, grow in dense spikes, and are 
enn'nal. This plant is perennial, grows wild 
n meadows and pasture-grounds, and flowers 
in June and July. This herb is recommended 
as a mild restringent and vulnerary in spittings 
of blood, and other hemorrhages and fluxes; 
and in gargarisms against aphthae and inflam- 
mations of the fauces. Its virtues do not ap- 
pear to be very great; to the taste it disco- 
vers a very slight austerity or bitterishness, 
which is more sensible in the flowery tops 
than the leaves. 
SELINUM, a genus of the digynia order, 
in the pentandria class of plants; and in the 
natural method ranking under the 45th or- 
der, umbellatae. The fruit is oval, oblong, 
compressed, plane, and striated in the mid- 
dle: t'ne involucrum is reflexed; the petals 
cordate and equal. There are nine species, 
the sylvestre, palustre, austriacum, carufolia, 
chabraci, seguieri, monnieri, sibiricum, and 
deceprens. 
SELL, in building, is of two kinds, viz. 
ground-sell, which denotes the lowest piece 
of timber, in a timber building, and that on 
which the whole superstructure is raised ; and 
the window-sell, called also window-soil, is 
the bottom pi ce in a window-frame. 
SELLA EQUINA. See Anatomy. 
SELTZER- WATER. See Waters, 
Mineral. 
SE M EC AR PUS, a genus of the trigynia 
order, in the pentandria class of plants. The 
corolla is quinquepetalous ; the drupa is 
heart-shaped, ceilulous, and monospermous. 
There is but one species. 
SEMEN, a substance prepared by nature 
for the reproduction and .conservation of the 
species both in animals and plants. The pe- 
culiar liquid secreted in the testes of males, 
and destined for the impregnation of females, 
is known by the name of semen. The human 
semen alone has hitherto been subjected to 
chemical analysis. Nothing is known con- 
cerning the seminal fluid of other animals. 
Vatiquelin published an analysis of the hit- 
man semen in 1791- 
Semen, when newly ejected, is evidently a 
mixture of two different substances: the one, 
fluid and milky, which is supposed to be se- 
creted by the prostate gland ; the other, 
which is considered as the true secretion of 
the testes, is a thick mucilaginous substance, 
in which numerous white shining filaments 
may be discovered. It has a slight disagree- 
able odour, an acrid irritating taste, and its 
specific gravity is greater than that of water. 
When rubbed in a mortar it becomes frothy, 
and of -the consistence of pomatum, in conse- 
quence of its enveloping a great number of 
air-bubbles. It converts paper stained with 
the blossoms of mallows or violets to a green 
colour, and consequently contains an al- 
kali. 
As the liquid cools, the mucilaginous part 
becomes transparent, and acquires greater 
consistency; but in about twenty minutes af- 
ter its emission, the whole becomes perfectly 
liquid. This liquefaction is not owing to the 
absorption of moisture from the air, for it 
loses instead of acquiring weight during its 
exposure to the atmosphere ; nor is it owing 
to the action of the air, for it takes place 
equally in close vessels. 
Semen is insoluble in water before tins 
spontaneous liquefaction, but afterwards it 
dissolves readily in it. Yv hen alcohol or 
oxymuriatic acid is poured into this solution, 
a number of white flakes are precipitated. 
Coricentrated alkalies facilitate its combina- 
tion with water. Acids readily dissolve the 
semen, and tile solution is not decomposed by 
alkalies; neither indeed is the alkaline solu- 
tion decomposed by acids. 
Lime disengages no ammonia from fresh se- 
men ; but after that fluid has remained for 
some time in a moist and warm atmosphere, 
lime separates a great quantity from it. Con- 
sequently ammonia is formed during the ex- 
posure of semen to the air. 
When oxymuriatic acid is poured into se- 
men, a number of white flakes precipitate, 
and the acid loses its peculiar odour. These 
flakes are in oluble in water, and even in acids. 
If the quantity of acid is sufficient, the semen 
acquires a yellow colour. Thus it appears 
that semen contains a mucilaginous substance 
analogous to that of the tears, which coagu- 
lates by absorbing oygen. M. Vauquelin 
obtained from 100 parts of semen six parts of 
this mucilage. 
When semen is exposed to the air about 
the temperature of 60°, it becomes gradually 
covered with a transparent pellicle, and in 
three or four days deposits small transparent 
crystals, often crossing each other in such a 
manner as to represent the spokes of a w heel. 
These crystals, when viewed through mi- 
croscope," appear to be four-sided prisms, 
terminated by very long four-sided pyramids. 
They may be separated by diluting the liquid 
with" water, and decanting it off They have 
all the properties of phosphat of lime. If, 
after the appearance of these crystals, the se- 
men is still allowed to remain exposed to the 
atmosphere, the pellicle on its surface gradu- 
ally thickens, and a number of white round 
bodies appear on different parts of it. These 
bodies also are phosphat of lime, prevented 
from crystallizing regularly by tire too rapid 
abstraction of moisture. M. Vauquelin found 
that 100 parts of semen contain three parts of 
phosphat of lime. If at this period of the 
evaporation the air becomes moist, other 
crystals appear in the semen, which have the 
properties of carbonat of soda. The evapo- 
ration does not go on to complete exsicca- 
tion, unless at the temperature of 77°, and 
when the air is very dry. When all the mois- 
ture is evaporated, the semen has lost 0.9 of 
its weight ; the residuum is semitransparent 
like horn, and brittle. 
When semen is kept in very moist air, at 
the temperature of about 77°, it acquires a 
yellow colour, like that of the yolk of an egg; 
its taste becomes acid, it exhales the odour of 
putrid fish, and its surface is covered with 
abundance of the byssus septica. 
When dried semen is exposed to heat in a 
crucible, it melts, acquires a brown colour, 
and exhales a yellow fume, having the odour 
of burnt horn. When the heat is raised, the 
matter sw ells, becomes black, and gives out a 
strong odour of ammonia. When the odour 
of ammonia disappears, if the matter is lixivi- 
ated with water, an alkaline solution may be 
obtained, which, by evaporation, yields crys- 
tals of carbonat of soda. M. Vauquelin 
found that 100 parts of semen contain one 
part of soda. If the residuum is incinerated, 
there will remain only a quantity of white 
ashes, consisting of phosphat of lime. 
