78 POLYGALE^. 



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 cylin- 

 .drical 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 wo'odj'^ portion being either pene- 

 trated by clefts or wide notches, or one-half or even more is altogether 

 wanting, the space where Avood 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) ex- 

 tracted 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 for- 

 mulas 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 authori- 

 ties, 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, 



