ESCULENT AND MEDICINAL LICHENS.

571

merce, portions of the epidermis and meso-thallus of some lichen are found.My colleague , Mr. Quekett , who has carefully examined them, cannot de-cide whether they be the tissues of liocella or of Lecanora. The preciseHiode of obtaining litmus is not known ; but there is little doubt the pro-cess is somewhat analogous to that for making orchil. The lichen iss aid to be fermented in putrid (distilled ?) urine. The substance whichyields the blue colour is either identical with, or very analogous to,er ythrin.

Properties and Uses of Litmus. —Litmus occurs in small, cubical,%ht, and friable cakes of a dirty blue colour. Examined by themicroscope, we find sporules, and portions of the epidermis and meso-

alius of some species of lichen, moss leaves, silica, &c. When the cakesar e thrown into dilute hydrochloric acid, effervescence takes place, anda solution of chloride of calcium is obtained, shewing that they containc arbonate of lime. The blue colouring matter of litmus is soluble in both" ater and alcohol. It is reddened by acids, but restored by alkalies.Chlorine and the hypochlorites destroy it. Tincture of Litmus is pre-pared by digesting one part of litmus in about twenty-five parts of water.Wue test paper (charta exploratoria carulea, Ph . Bor.) is made withbibulous or unsized paper, which is to be brushed over with, or immersedlri > a filtered infusion of litmus (composed of one part litmus and fourParts water), and when carefully dried, preserved in a well-stopped vessel111 a dark cupboard. Both tincture and paper are used as tests for freeaci ds: the former requires to be diluted before it is employed.

Other Esculent and Medicinal Lichens.

Fig. 74. Fig. 75.

Tripe de Roche.

mmm

Cladonia rangiferina.

l Cv oral species of Gyrophora (as G. proboscidea and cylindrica) are employed by ther 0 d er s of the Arctic regions of America as articles of food, under the name of tripe defor** 74). They supported Capt. Sir John Franklin and his companions in 182110s nian -V d ays. The bitter principle proved noxious to several of the party (Narrative,. Cladonia rangiferina or rein-deer moss (fig. 75) is a well-known example of a^ lichen, supporting the animals after whom it is named when no other sustenance

affi* ev . er al lichens are employed as popular remedies for hooping-cough and pulmonary®«t| C i ns ‘ Those usually kept by the herbalist are, Sticta pulmonaria (called oak lungs),YfJ'f^Phorus pyxidatus (cup moss), and Peltidea canina (sold as ground liverwort). The"■as formerlv thought to be a specific for hydrophobia.