SENNA TREE. 137 



straws and other substances to receive the flowing juice, the manna 

 becomes much improve^ : Houel, who tasted 'the manna when flow- 

 ing from the tree, found it much bitterer than in its concrete state; 

 this bitterness he attributes to the aqueous part, which is then very 

 abundant, of course the manna is meliorated by all the circumstances 

 which promote evaporation. According to Lewis, " the best manna 

 is in oblong pieces, or flakes, moderately dry, friable, very light, of 

 a whitish or pale yellow colour, and in some degree transparent : the 

 inferior kinds are moist, unctuous, and brown. Manna liquifies in 

 rnoi>t air, dissolves readily in water, and, by the assistance of heat, in 

 rectified spirit. On inspissating the watery solution, the manna is 

 recovered of a much darker colour than at first. From the saturated 

 spirituous solution, great part of it separates as the liquor cools, con- 

 creting into a flaky mass, of a snowy whiteness, and a very grateful 

 sweetness." 



Manna is well known as a gentle purgative, so mild in its opera- 

 tion, that it may be given with safety to children and pregnant wo- 

 men ; in some constitutions however it produces troublesome flatu- 

 lencies, aud therefore requires the addition of a suitable aromatic, 

 especially when given to an adult, where a large dose is necessary ; it 

 is therefore usually actuated by some other cathartic of a more 

 powerful kind. The efficacy of manna is said, by Vallisnieri, to be 

 much promoted by cassia fistularis, a mixture of the two purging 

 more than both of them separately ; it is therefore very properly an 

 ingredient in the electuarium e cassia. 



[IVoodville. Cullen. IIort.Kew. 



SECTION. II 



Senna'Tree. 



Cassia Senna. Linn. 



Cassia in the Linnaean system is a voluminous genus, comprehend- 

 ing not fewer than fifty-four or fifty-six species; of these there are 

 two that furnish useful materials in medicine. C. senna, which be- 

 longs to the present section, and C. Fistula, which will be described 

 in the next. 



The root of this plant is annual : the stalk is strong, smooth, 

 branched, erect, and rises about two feet in height : the leaves stand 

 in alternate order, and at their base are placed narrow pointed sti. 



