CASTOR 



183 



Castor seeds have an almost imperceptible odour and very slightly 

 acrid taste. 



The student should observe 



(a) The glossy, mottled seed-coat, 



(b) The small caruncle, 



(c) The oily endosperm and papery cotyledons ; 



and compare the seeds with croton seeds, which have a uniformly 

 dull brown surface. 



Constituents. The most important medicinal constituent of 

 castor seed is the fixed oil. It exists in the seed to the extent of 

 about 50 per cent., and may be obtained by pressing the unshelled 

 or shelled seed without heat (' cold drawn castor oil'). Usually the 

 seeds are first graded to size, 

 cracked between rollers, the 

 shells removed by fanning 

 and the kernels pressed ; the 

 oil is filtered, steamed to 

 coagulate proteids (see be- 

 low) and again filtered. The 

 cake still contains 8 to 10 

 per cent, of oil which can 

 be recovered by extraction 

 with benzene. Much is thus 

 produced in Italy, Marseilles, 

 London, Hull, Belgium, &c. Fia - 98. Fruit and seed of Ricinus communis. 

 Considerable quantities are Natural size ' < Bentle y and Trimen '> 



also produced in India and 



elsewhere by pressing the seeds between hot plates, or by boiling 

 the crushed seeds and skimming off the oil, but such oil has a 

 dark colour and disagreeable odour, and is unsuitable for medi- 

 cinal use. 



The cake left after the expression of the oil contains ricinine 

 (Tuson, 1864), a crystalline principle melting at 201-5, but present 

 in small quantity only (about 0'2 per cent.), ricin (Stillrnark, 1889), a 

 toxin similar in nature to the bacterial toxins, and also (ripe seeds) 

 a very active lipase (fat-splitting enzyme) and other enzymes. 



Both castor seeds and the cake left after the expression of the oil 

 act as violent purgatives, a property probably due to the ricin 

 contained in them. 



Castor oil consists chiefly of the glycerides of ricinoleic, isoricinoleic dihydroxy- 

 stearic, and other acids. It owes its purgative action in all probability to 

 the ricinoleic acid. It is characterised by its specific gravity (0-958 to 0-970), 

 solubility in alcohol (1 in 3-5), insolubility in petroleum spirit (which, however, 

 disappears if other vegetable oils are present) and by its high acetyl value (150). 



