This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
The slippery elm, Ulmus fulva, Michaux (N.O. Urticaceoe), is a small tree indigenous to the central and northern United States. The bark is collected in the spring from the trunk and large branches, deprived of its outer dead portions, and dried; the tree is thereby destroyed, and as the wood has no commercial value no effort is made to replace it. Large quantities of the bark are collected in the lower peninsula of Michigan.
The slippery elm bark of commerce consists entirely of secondary bast. It is commonly imported in large flat strips half to one metre long, but only 3 mm. or less in thickness. The outer surface is reddish yellow in colour, with patches of the reddish brown outer portion (bark), and is distinctly striated longitudinally; the inner surface is tawny yellow and also longitudinally striated.
It is extremely tough and fibrous. The section, examined under the lens, is seen to be completely traversed by medullary rays, between which small tangential bands (bast fibres and bast parenchyma) are arranged, giving the section a chequered appearance. If the transverse section is moistened and allowed to remain for a minute or two and again examined, numerous cells full of transparent swollen mucilage can be detected. No trace of the cortex can be found, but portions of the dark outer layer (bark) are frequently present.
The bark has a strong odour resembling fenugreek, and a very mucilaginous taste.
The student should observe
(a) The striated inner and outer surface,
(b) The fibrous fracture,
(c) The odour of fenugreek and the mucilaginous taste; and should compare the bark with
Quillaja bark, which has a splintery fracture, a smooth inner surface, and is odourless.
The principal constituent is mucilage, which appears to swell but not dissolve in water; it is contained in large mucilage cells in the bast, and is present in such proportions that 1 gm. of the powdered bark will convert 50 c.c. of water into a thick jelly.
The bark has demulcent and emollient properties. It is chiefly used as an external application in the form of a poultice.