ALOES 437 



barbaloin and isobarbaloin. /3-barbaloin is particularly abundant 

 in Cape and Uganda aloes. 



Other constituents of aloes are resin and aloe-emodin, in addition 

 to water-soluble substances (other than the aloins) of which nothing 

 definite is known. The resin of Curagao aloes consists of barbalore- 

 sinotannol combined with cinnamic acid ; that of Cape, Uganda, 

 Natal, and probably Zanzibar and Socotrine aloes consists of capa- 

 loresinotannol combined with paracumaric acid. 



Aloe-emodin is a decomposition product of barbaloin and occurs 

 in small proportion only. 



Various formulae have been proposed for barbaloin of which that of L6ger, 

 C 21 H 20 9 , is probably the most correct. It is sparingly soluble in water, more 

 readily in alcohol and acetone. Its aqueous solution slowly acquires a green 

 fluorescence when saturated with borax. It is a glucosidal methylanthra- 

 quinone derivative, yielding by prolonged standing of an alcoholic solution, 

 or by treatment with sodium peroxide (but not with mineral acids), aloe-emodin 

 and d-arabinose. It is isomeric with frangulin (compare p. 245), but the latter 

 is hydrolysed by mineral acids yielding rhamnose. 



The proportion in which the aloins are present in the respective 

 aloes is not accurately known. Tilden (1872) and Treumann (1880) 

 obtained from 20 to 25 per cent, of aloin from Curacao aloes. Carr 

 and Reynolds (1907) found in a number of specimens from 12*6 to 27 '9 

 per cent. As no exact assay process is known, and as there appears 

 to be considerable loss in its extraction, it may be assumed that good 

 Curagao aloes may contain upwards of 30 per cent, of crystallisable 

 aloins. Socotrine and Zanzibar aloes appear to contain less. Cape 

 aloes has yielded over 9 per cent. 



Natal aloes differs materially from other aloes in its composition. 

 It contains nataloin, homonataloin, and a resin consisting of nataloresi- 

 notannol (probably identical with capaloresinotannol) combined with 

 paracumaric acid. Nataloin does not yield a fluorescent solution when 

 dissolved in a solution of borax. 



Uses. All the varieties of aloes have more or less powerful purgative 

 action, Cape aloes being the strongest and Natal aloes the weakest, 

 all of them acting with remarkable slowness. Aloes is one of the most 

 valuable purgatives in certain forms of constipation, as it improves 

 the digestion and does not lose in activity by repetition. 



Varieties. In addition to the above-described varieties Mocha aloes 

 is occasionally imported from Bombay in tin-lined cases ; it is a black, 

 brittle, glassy aloes of very strong odour and inferior quality, 

 Jafferabad aloes, which is sent from that port to Bombay, is also 

 nearly black ; it does not enter into English commerce. 



