200 MATER i A MEDIC A AND THERAPEUTICS. 



developed by a decomposition of their constituents. On the 

 addition of water to the black mustard, its most important 

 principle, potassium myronate or sinigrin (C in H 18 NKS 2 10 ), a 

 compound of potassium with an acid glucoside, tnyronic acid, 

 is broken up by another constituent, myrosin, a ferment, into 

 volatile oil of mustard, potassium sulphate, and sugar, thus : 

 K,C 10 H 18 NS 2 10 = C 4 H 5 NS + KHS0 4 + C 6 H 12 6 . Sinapis 

 alba also contains the fixed oil. It does not, however, yield the 

 volatile oil, but a substance with allied properties, called sulpho- 

 cyanate of acrinyl, C 8 H 7 NSO, by a similar decomposition of its 

 constituents, sinalbin, C 30 H 44 N 2 S 2 16 (in place of potassium 

 myronate) and myrosin, thus : C 30 H 44 N 2 S 2 Oj 6 = C 8 H 7 NSO + 

 C 16 H23N0 5 ,H 2 S0 4 (disulphate of slnapin) -f C 6 H 12 6 (glucose). 



Preparations. 



1. Oleum Sinapis. The oil distilled with water from the seeds 



of Sinapis nigra after the expression of the fixed oil. 

 Solubility, 1 in 50 of water ; readily in spirit and ether. 



From Oleum Sinapis is prepared : 



a. Linimentum Sinapis Compositum. 1 in 41, with 

 Ethereal Extract of Mezereon, Camphor, Castor Oil, 

 and Spirit. 



2. Cataplasma Sinapis. Mustard in powder, linseed meal, 



and boiling water. 



3. Charta Sinapis. Made with guttapercha solution. 



ACTION AND USES. 

 1. IMMEDIATE LOCAL ACTION AND USES. 



Externally. When applied to a limited area of skin 

 mustard acts quickly (1) as a rubefacient and nervous stimu- 

 lant, causing redness, heat, and severe burning pain. (2) This 

 effect is speedily followed by loss of sensibility in the 

 part to other impressions, and relief of previous pain. (3) The 

 prolonged application of the charta or cataplasm causes vesi- 

 cation by the production of local inflammation. Neighbouring 

 and deeper parts, and viscera in vascular communication or 

 intimate nervous relation with the blistered area, may thus 

 have their circulation relieved. The heart, blood pressure, 

 respiration, and nervous centres generally are stimulated by 

 the first application of mustard to the skin ; soothed during the 

 stage of anaesthesia, and relief of pain ; and depressed in the 

 third stage, especially if the vesication be severe through 



