FOXGLOVE 65 



(c) The simple unbranched hairs, 



(d) The course taken by the lateral veins ; 



and should compare these leaves with 



(i) Matico leaves, in which the veinlets are depressed on the 



upper surface, dividing it into small squares, 

 (ii) The possible substitutions mentioned below. 



Constituents. Although the constituents of foxglove have 

 repeatedly been the subject of research, our knowledge of them 

 remains incomplete. The activity of the leaves appears to be due 

 chiefly to digitoxin, digitalein (gitalin, Kraft) and digitophyllin ; 

 other constituents are saponins, digitoflavone (luteolin), an irritant 

 resin (digitalic acid), and a very active oxydase. 



Digitoxin, CgjH^On, is a well-defined, colourless, odourless, crystalline, 

 bitter substance, insoluble in water, but nevertheless passing into solution 

 in appreciable quantity when foxglove leaves are infused in that menstruum. 

 It is the most toxic of the active constituents of the leaves, and is cumulative 

 in action, being apparently fixed by the muscles of the heart. It is hydrolysed 

 by dilute mineral acids yielding digitoxigenin, C 22 H 32 O4, and a sugar, digitoxose, 

 C 6 H 12 O 4 . It may be identified by Keller's reaction, which consists in dissolving 

 it in glacial acetic acid, adding a drop of ferric chloride solution, and then gently 

 a stratum of sulphuric acid ; the upper part of the latter is coloured red, whilst 

 above this an indigo blue band gradually appears. 



Dry foxgloves leaves contain from 0*2 to 0-3 per cent, of digitoxin, the first 

 year's leaves containing as much as the second. Wild plants contain more 

 than cultivated, but the quantity rapidly diminishes towards the end of the 

 flowering stage. 



Digitalein (0'3 to 0*9 per cent.), a purified form of which is known as gitalin, 

 is an amorphous, in hydrated form crystalline, glucoside soluble in water ; it 

 has a marked action on the heart and as it is not cumulative it is believed to 

 be more valuable therapeutically than digitoxin. It passes readily into the 

 infusion. By heating it changes into anhydrogitalin and by hydrolysis it 

 yields anhydrogitaligenin and digitoxose. 



Digitophyllin, crystallising in plates melting at 232, is probably methyl- 

 digi toxin and gives the same colour reaction as digitoxin. 



Digitoflavone, (luteolin) is a yellow colouring matter allied to quercetin. 



The saponins appear to- comprise digitsaponin, amorphous, soluble hi water 

 and gitin, crystalline and insoluble in water. The digitsaponin accelerates 

 the heart-beat but is non-cumulative. 



The active constituents of foxglove seeds are : 

 Digitoxin (see above). 



Digitalin, a crystalline, water-soluble, active glucoside not identical with 

 digitalein. 



Digitonin, a crystalline saponin resembling gitin but not identical with it. 



The digitalins of commerce appear to be variable mixtures : 



Homolle's digitalin is amorphous and a mixture of digitoxin and digitalin. 



Nativelle's digitalin is crystalline and chiefly digitoxin. 



