680 



MEDICAL BOTANY. 



Cetraria islandica. — Thallus erect, tufted, olive-brown, paler on one side, laciniated, 

 channelled, and dento-ciliate ; the fertile lacinise very broad. Shields brown, appressed, 

 flat, with an elevated border. 



This is found in exposed situations, in northern countries, in both hemi- 

 spheres. When dried it has no odour, and a mucilaginous, slightly bitter 

 taste. It is a mucilaginous or demulcent tonic, with no astringency, and has 

 been thought useful in pulmonary complaints, when freed from the bitter 

 principle by steeping in a weak alkaline solution. It is capable of forming a 

 jelly by boiling in water or milk; this jelly, when properly flavoured, forms 

 an agreeable and nutritious diet. In the fresh state, and without any prepa- 

 ration, Sir John Franklin found that it was scarcely eatable, from its great 

 bitterness, though he and his party were then suffering great privations (Nar- 

 rative, 414). 



Sticta pulmonaria has much the same properties, and has obtained some 

 reputation as a remedy in pulmonary affections. Its nutritive qualities are 

 not as great as those of the Cetraria. Gyrophora proboscidia and G. cylin- 

 drica, natives of the more northern regions, are used by hunters and travel- 

 lers in the Arctic regions as articles of f6od, under the name of Tripe de 

 Roche. These are nutritious, but unpleasantly bitter, and often cause severe 

 colic and other affections of the digestive organs (Long's Second Expedit.) 

 Peltidea aphthosa is said to be purgative and anthelmintic, and several species 

 of Variolaria to be useful as febrifuges in intermittent fevers ; as is also Par- 

 melia parietina. Borrera furfuracea is in like manner reputed to be astrin- 

 gent and febrifuge, which is also the case with some species of Scyphophorus. 

 Several species of Cladonia are also used : the C. sanguinea, according to 

 Martius, is much esteemed in Brazil as a remedy for aphthae in children, for 

 which purpose it is rubbed down in sugar and water ; C. vermicularis is used 

 in the same country as a stomachic, and is called Contrayerba blanca. The 

 best known, however, is the Cladonia rangiferina, or Reindeer Moss. This 

 species is very nutritious, and has very little of the bitterness of most of the 

 Lichens. It forms the principal food of the Reindeer during the winter, and 

 is also eaten by the Icelanders and Laplanders, who form jellies from it by 

 boiling it with milk. 



Fig. 333. 



Fig. 334. 



C. rangiferina. 



L. tartarea. 



Some of the Lichens are much used in the arts, as affording dyes. This 

 is owing to the presence of a peculiar principle, called usnine or usnic acid, 

 which exists in them, accompanied by yellow and green resins, and which, 

 with them, have the property of becoming of various shades of colour when 



