ON CINCHONA. 
251 
given to a brown epidermis by some crustaceous lichens, for 
a genuine white epidermis. The term warty or knotty 
{Cinchona nodosa of Bergen) is applied to those barks in 
which we observe prominences on the epidermis, correspond- 
ing to elevations on the subjacent parts. These are frequently 
observed in some specimens of red bark, as well as in the kind 
called Huamalies. Barkis termed cracky or furrowed {Cin- 
chonarimosa of Bergen) when we observe cracks or furrows (the 
latter may be regarded merely as larger kinds of cracks) on it. 
When we observe longitudinal or transverse elevations, we 
say the bark is wrinkled {Cinchona rugosa.) 
{b.) Bete mucosum — cellular envelope — medulla — ex- 
terna. — This is a cellular layer, placed immediately beneath 
the epidermis. It is tasteless, and is of no medicinal value. 
In old barks, (particularly old red bark) it is often much de- 
veloped: in uncoated bark it is sometimes, though not always 
absent. 
(c.) Cortical layers or cortex. These are beneath the rete 
mucosum, and, in fact, form the essential part of the bark. 
One layer is formed annually, and hence their number, and 
consequently the thickness of the bark depends on the age of 
the tree from whence it is taken. The last formed layer, that 
which is in the innermost, is termed liber. Every one of the 
cortical layers has medicinal virtue, but the liber the most. 
The reason for this will be readily comprehended by re- 
ference to the physiology of exogenous plants. The succus 
communis of these plants ascends by the alburnum, or sap 
wood, to the leaves, where it undergoes certain changes by 
the agency of the atmosphere, in consequence of which it is 
converted into what is called succus proprius, the proper 
juice of the plant, and in which any medicinal activity which 
the latter possesses usually resides. Now this succus proprius 
descends in the liber: hence this part may always be expected 
to possess the proper medicinal activity of the tree from 
whence it is taken. 
Cry ptogamic plants. — The epidermis of Cinchona barks is 
frequently covered, either wholly or partially, by cryptogamic 
