_Radix Senekæ_; _Senega or Seneka Root_; F. _Racine de Polygala de
Virginie_; G. _Senegawurzel_.
=Botanical Origin=—_Polygala Senega_ L., a perennial plant with slender
ascending stems 6 to 12 inches high, and spikes of dull white flowers
resembling in form those of the Common Milkwort of Britain. It is found
in British America as far north as the river Saskatchewan, and in the
United States from New England to Wisconsin, Kentucky, Tennessee,
Virginia and the upper parts of North Carolina, as well as in Georgia
and Texas, not in the Rocky Mountains.
The plant, which frequents rocky open woods and plains, has become
somewhat scarce in the Atlantic states, and as a drug is now chiefly
collected in the west, the plant growing profusely in Iowa and
Minnesota, west of New York.
=History=—The employment of this root among the Seneca Indians as a
remedy for the bite of the rattlesnake attracted the notice of Tennent,
a Scotch physician in Virginia; and from the good effects he witnessed
he concluded that it might be administered with advantage in pleurisy
and peripneumonia. The result of numerous trials made in the years
1734 and 1735 proved the utility of the drug in these complaints, and
Tennent communicated his observations to the celebrated Dr. Mead of
London in the form of an epistle, afterwards published together with an
engraving of the plant, then called the _Seneca Rattlesnake Root_.[325]
Tennent’s practice was to administer the root in powder or as a strong
decoction, or more often infused in wine. The new drug was favourably
received in Europe, and its virtues discussed in numerous theses and
dissertations, one written in 1749 being by Linnæus.[326]
=Description=—Senega root is developed at its upper end into a knotty
crown, in old roots as much as an inch in diameter, from which
spring the numerous wiry aerial stems, beset at the base with scaly
rudimentary leaves often of a purplish hue. Below the crown is a simple
tap-root ²/₁₀ to ³/₁₀ of an inch thick, of contorted or somewhat spiral
form, which usually soon divides into 2 or 3 spreading branches and
smaller filiform rootlets.
[324] Waring, _Pharm. of India_, 1868. 27.
[325] Tennent (John), _Epistle to Dr. Richard Mead concerning the
epidemical diseases of Virginia_, &c., Edinb. 1738.
[326] _Amœnitates Academicæ_, ii. 126.
The bark is light yellowish-grey, translucent, horny, shrivelled,
knotted and partially annulated. Very frequently a keel-shaped ridge
occurs, running like a shrunken sinew through the principal root;
it has no connexion with the wood, but originates in a one-sided
development of the liber-tissue. The bark encloses a pure, white woody
column about as thick as itself. After the root has been macerated in
water the bark is easily peeled off, and the peculiar structure of
the wood can then be studied. The latter immediately below the crown
is a cylindrical cord, cleft however by numerous, fine, longitudinal
fissures. Lower down these fissures increase in an irregular manner,
causing a very abnormal development of the wood. Transverse sections
of a root therefore differ greatly, the circular wood portion being
either penetrated by clefts or wide notches, or one-half or even more
is altogether wanting, the space where wood should exist being in each
case filled up by uniform parenchymatous tissue.
Senega root has a short brittle fracture, a peculiar rancid odour, and
a very acrid and sourish taste. When handled it disperses in irritating
dust.
=Microscopic Structure=—The woody part is built up of dotted vessels
surrounded by short porous ligneous cells; the medullary rays consist
of one or two rows of the usual small cells. There is no pith in the
centre of the root. The clefts and notches are filled up with an
uniform tissue passing into the primary cortical tissue without a
distinct liber; the large cells of this tissue are spirally striated.
In the keel-shaped rider the proper liber rays may be distinguished
from the medullary rays. The former are made up of a soft tissue, hence
the cortical part of the root breaks short together with the wood.
Neither starch granules nor crystals of oxalate of calcium are present
in this root; the chief contents of its tissue are albuminoid granules
and drops of fatty oil.
=Chemical Composition=—The substance to which the drug owes its
irritating taste was distinguished by the name of _Senegin_ by Gehlen
as early as 1804, and is probably the same as the _Polygalic Acid_ of
Quevenne (1836) and of Procter (1859). Christophsohn (1874) extracted
it by means of boiling water, evaporated the solution and exhausted
the residue with boiling alcohol (0·853 sp. gr.). The liquid after a
day or two, deposits the crude senegin, which is to be washed with
alcohol (0·813 sp. gr.), and again dissolved in water, from which it
is precipitated by a large excess of hydrate of baryum. The barytic
compound, dissolved in water, is decomposed by carbonic acid, by which
carbonate of baryum is separated, senegin remaining in solution. It
is lastly to be precipitated by alcohol. It is amorphous, insoluble
in ether and in cold water; it forms with boiling water a frothing
solution. Like saponin, to which it is very closely allied, it excites
violent sneezing.
Dilute inorganic acids added to a warm solution of senegin throw down
a flocculent jelly of _Sapogenin_, the liquid retaining in solution
uncrystallizable sugar. Alkalis give rise to the same decomposition;
but it is difficult to split up the senegin completely, and hence the
formulas given for this process are doubtful. Even the formula of
senegin itself is not definitely settled. According to Christophsohn,
the root yields about 2 per cent. of this substance; according to
earlier authorities, who doubtless had it less pure, a much larger
proportion. From Schneider’s investigations (1875) it would appear that
the rootlets are richest in senegin.
Senega root contains a little volatile oil, traces of resin, also gum,
salts of malic acid, yellow colouring matter, and sugar (7 per cent.
according to Rebling, 1855). The _Virginic Acid_ said by Quevenne to
be contained in it, and the bitter substance _Isolusin_ mentioned by
Peschier, are doubtful bodies.
=Uses=—Senega is prescribed as a stimulating expectorant and diuretic,
useful in pneumonia, asthma and rheumatism. It is much esteemed in
America.
=Adulteration=—The drug is not liable to be wilfully falsified, but
through careless collecting there is occasionally a slight admixture of
other roots. One of these is American Ginseng (_Panax quinquefolium_
L.) a spindle-shaped root which may be found here and there both in
senega and serpentaria. The rhizome of _Cypripedium pubescens_ Willd.
has also been noticed; it cannot be confounded with that of _Polygala
Senega_. The same may be said with regard to the rhizome of _Cynanchum
Vincetoxicum_ R. Brown (_Asclepias_ L., _Vincetoxicum officinale_
Mönch).