SEM 
Ptolemies did in Egypt. This jera we find 
expressed in the book of the Maccabees, 
and on a great number of Greek medals, 
struck by the cities of Syria, &c. The rab- 
bins call it the sera of contracts ; and the 
Arabs therik dilkarnain, that is, the sera of 
the two horns. According to the best ac- 
counts, the first year of this sera fells in the 
year 311 before Christ, being twelve years 
after Alexander’s death. 
SELINUM, in botany, a genus of the 
Pentandria Digynia class and order. Na- 
tural order of Umbellatae or Umbelliferse. 
Essential character : petals, cordate, equal ; 
involucre, reflex; fruit oval, oblong, com- 
pressed, flat, striated in the middle. There 
are nine species. 
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, is the bottom piece 
in a window-frame. 
SEMECARPUS, in botany, a genus of 
the Pentandria Trigynia class and order. 
Essential character: calyx inferior, five- 
cleft ; corolla, five petalled ; nut, kidney- 
form, inserted into a large fleshy, flattened 
receptacle. There is but one species, viz. 
S. anacardium, marking nut tree. It is a 
native of all the mountainous parts of India, 
flowering in July and August. 
SEMEN. See Physiology. Semen 
is secreted in the testes of male animals ; 
but when it is qected it is composed of 
two substances; the one is fluid and milky, 
and the other of a thick mucilaginous con- 
sistence, in which appear a great number 
of white silky filaments, especially if it 
be agitated in, cold water. It has a dis- 
agreeable odour, and an acrid irritating 
taste. The specific gravity varies consider- • 
ably, but is always greater than that of 
water. When it is rubbed in a mortar, it 
froths up, and acquires the consistence of 
pomatum from the air with which it mixes. 
It converts the flowers of violets, to a green 
colour, and it precipitates the calcareous 
and metallic salts, which shows, that it 
contains an uncombined alkali. The thick ' 
part of tlie semen as it cools, becomes 
transparent, and assumes a greater degree 
of consistence ; but it afterwards becomes 
entirely liquid, even -without absorbing 
moisture from air. If semen be exposed 
to the air after it has become liquid at the 
temperature of sixty degrees, it becomes 
covered with a transparent pellicle, and at 
the end of three or four days deposits fine 
SEM 
transparent crystals of a line in lengtii 
crossing each other like radii from a centre! 
When they are magnified, they appear to 
be four-sided prisms terminated by long 
four-sided pyramids^ When semen is ex- 
posed to a warm air, in considerable quan- 
tity, it is decomposed ; it assumes the colour 
of the yolk of egg, and becomes acid, either 
by absorbing the oxygen from the atmos- 
phere, or by a different combination and 
arrangement of its own constituent prin- 
ciples. Heat accelerates the liquefaction 
of semen; and when it has undergone tl)is 
change it is no longer susceptible of coagu- 
lation. It is decomposed by the applica- 
tion of strong heat. Water is first sepa- 
rated ; it then blackens, swells up, and 
emits yellow fumes, having an empyreu- 
matic, ammoniacal odour. Alight coal re- 
mains behind, which burns readily to white 
ashes. 
The acids readily dissolve semen, and 
this solution is not decomposed by the al- 
kalies ; nor indeed is the alkidine solution 
of semen decomposed by the acids. M'^ine, 
cider, and urine, also dissolve semen, but 
it is in consequence of the acid which is 
combined with these liquids. The crystals 
which form in semen by spontaneous eva- 
poration in the open air, and which are en- 
tangled in the viscid matter, may be sepa- 
rated by adding water. 
These crystals have neither smell nor 
taste. They melt under the blow-pipe into 
a white opaque globule, which is surrounded 
with a yellowish flame. This salt is insolu- 
ble in water, and is not acted on by the 
alkalies; but is soluble in the mineral acids 
without effervescence, from which solutions,; 
lime water, the alkalies, and oxalic acid 
throw down a precipitate. The component 
parts of semen are found to be 
Water go 
Mucilage o 
Soda 1 
Phosphate of lime 3 
100 
SEMICIRCLE, in geometry, half a cir- 
cle, or that figure comprehended between 
the diameter of a circle and half the circum- 
ference. - 
SEMICOLON, in grammar, one of the 
points or stops used to distinguish the seve- 
ral members of sentences from each other. 
See Punctuation. 
SEMICUBICAL paraliola, in the higher 
geometry, a curve of the second order^ 
