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Materia Meclica.

Part II.

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bodies, internally of a brown colour: these are the pericar-piums. When fresh, the colour of this lichen is greenish-yel-low, or greyish-brown ; but when dried, greenish-white orgrey. In Sweden principally, and in Germany, a variety isfound, with smaller, tenderer, crisper leaves, destitute of hairson the margin, of a paler lead colour, orange beneath. It isgathered in rainy weather, because it is then more easily de-tached from the stones. In the countries where it abounds,it is used for the nourishment both of cattle and of man. MrProust has analyzed it with much success. A pound of drylichen immersed in cold -water soon resumed its fresh colour,and weighed two pounds two ounces, gave out a pale fawn co-lour to the water, but none of its bitterness. When previous-ly powdered, it gives out a bitter, pale, yellow juice, losing a-bout three per cent, in cold, and six in boiling water. Thisbitterness resides in an extractive, which is employed in Ice-land to dye a brown colour. By boiling lichen a quarter ofan hour, it becomes sufficiently tender for use as an esculentvegetable. Lichen cooked in this manner has a kind of mem-branous elasticity, peculiar to some of the alga; and fungi;and after being dried, has only to be moistened with boilingwater to resume this elasticity. Its appearance is not veryprepossessing, having an unequal yellow colour, and a slightmarine smell, A pound of dry lichen by boiling weighs threepounds, and when dried again, is reduced to two-thirds of apound.

The decoction has a clear yellow colour, and a slightly bit-ter taste, which, even when made with eight waters, on cool-ing becomes a tremulous jelly, without any viscidity. Thisjelly on standing, contracts, expresses the water, cracks, anddries into transparent angular fragments, of a deep red colour,insoluble in co]d water, soluble in boiling water, from whichit is precipitated by infusion of galls. By nitric acid it is con-verted into oxalic acid. The insoluble part dissolves readilyin nitric acid, forming oxalate of lime and oxalic acid, and isconverted into a gelatinous pulp by potass.

According to this analysis, one hundred parts of dried li-chen give, of

Bitter extractive, 3

Matter soluble in hot water, 33

Matter insoluble in hot water, 64= 100

The last substance has much analogy with gluten, and thesecond with starch, particularly in the remarkable property ofbeing precipitated by infusion of galls. It differs from it, how-ever, in not being glutinous, and. in the solid matter of the

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