PDF - CES (IISc)

CELLS AND CELL PRODUCTS 221
an excretion in the cells of hepatics. He grew various species in which oilcells
occurred in the dark and then tested the cell contents. He found that
after three months of conditions in which the formation of new carbohydrates
was excluded, the oil in the cells, instead of having served as reserve material,
was entirely unchanged and must in that instance be regarded as an
excretion.
D. LICHEN-ACIDS
a. HISTORICAL. The most distinctive and most universal of lichen pro-
ducts are the so-called lichen-acids, peculiar substances found so far only in
lichens. They occur in the form of crystals or minute granules deposited in
greater or less abundance as excretory bodies on the outer surface of the
hyphal cells. Though usually so minute as scarcely to be recognized as
crystals, yet in a fairly large series their form can be clearly seen with a
high magnification. Many of them are colourless; others are a bright yellow,
orange or red, and give the clear pure tone of colour characteristic of some
of our most familiar lichens.
The first definite discovery of a lichen-acid was made towards the begin-
ning of the nineteenth century
and is due to the researches of C. H. Pfaff1 .
He was engaged in an examination of Cetraria islandica, the Iceland Moss,
which in his time was held in high repute, not only as a food but as a tonic.
He wished to determine the chemical properties of the bitter principle con-
tained in it, which was so much prized by the Medical Faculty of the period,
though the bitterness had to be removed to render palatable the nutritious
substance of the thallus. He succeeded in isolating an acid which he tested
and compared with other organic acids and found that it was a new substance,
nearest in chemical properties to succinic acid. In a final note, he states
that the new :<
lichen-acid," as he named it, approached still nearer to boletic
acid, a constituent of a fungus, though it was distinct from that substance
also in several particulars. The name " cetrarin " was proposed, at a later
date, by Herberger 2 who described it as a " subalkaloidal substance, slightly
soluble in cold water to which it gives a bitter taste; soluble in hot water,
but, on continued boiling, throwing down a brown powder which is slightly
soluble in alcohol and readily soluble in ether." Knop and Schnederman 3
found that Herberger's "cetrarin" was a compound substance and contained
besides other substances " cetraric acid " and lichesterinic acid. It has now
been determined by Hesse 4 as fumarprotocetraric acid (C