548 
THE PRINCIPLES OF BOTANY. 
which is used for coughs, and pulmonary complaints in 
general. 
That Lichens contain a large quantity of gum, and thus 
may be made into jellies or pates which are demulcent and 
softening to the throat, is quite true, but at the same time it 
is highly probable that their uses in coughs were originally 
pointed out on the fanciful doctrine of signatures, some of 
the forms being supposed to have the appearance of a lung, 
e.g., Sticta pulmonaria. Tree Lungwort was taken as Na- 
ture’s indication of its uses ; so the Pulmonaria officinalis 
(common Lungwort), a Boraginous flowering plant, was kept 
in our gardens for use in coughs, &c., on account of the 
spotted leaves reminding the observer of a section of a lung. 
But of all the species used in medicine, none has got so great 
a repute as the Cetraria Islandica (Iceland Moss), which, 
though an abundant plant on the Scotch mountains, is wholly 
imported for medicinal purposes from Norway and Iceland. 
Sir W. Hooker says of it, “ Immense quantities are gathered 
in the latter country, not only for sale, but for their own use 
as an article of common food. The bitter and purgative 
quality being extracted by steeping in water, the Lichen is 
dried, reduced to a powder, and made into a cake, or boiled 
and eaten with milk, and eaten with thankfulness, too, by 
the poor natives, who confess that c a bountiful Providence 
sends them bread out of the very stones.’ ” 
This leads us to consider this class of plants as articles of 
diet, but before doing so we must refer to the Peltidea canina 
(the ash-coloured ground Liverwort), which was formerly 
sold at the physic-shops and herbalists as a preservative 
against the bites of mad dogs, and, as stated by Pereira, 
mixed with half its weight of black pepper, it formed the 
pulvis antilyssus of the London Pharmacopoeia for 1721. This 
is said to have been formerly employed by Dr. Mead as a cure 
for the bite of a mad dog, whence its specific name ; but as 
we have none of the worthy doctor’s works to refer to, we 
are at a loss to determine the principle upon which he acted 
in using it. 
The uses of Lichens as food for man and some of the in- 
ferior animals have been long known. The hunters in the 
arctic regions of America eat some species of Gyrophora un- 
der the name of tripe de roche. Franklin and his companions, 
as he states in his Narrative, in 1821 partook of four species 
of the genus when suffering great privations in America ; 
and to its use their preservation is partly ascribed ; but as 
the bitter principle was not removed, the party suffered from 
severe bowel complaints. Probably, too, the mere fact that 
