Fig. 132. Pertusaria amara Nyl. on bark (S. H., Photo.).
One of the most frequently prescribed lichens was the tree lung-wort (Lobaria pulmonaria) ([Fig. 72]). It was first included among medical plants by Dorstenius[1274], a Professor at Marburg; he gives a good figure and supplies directions for its preparation as a cure for chest complaints. The doctrine of “signatures” influenced practitioners in its favour, but it contains lichenin which acts as an emollient. In England, it was taken up by the famous Dr Culpepper[1275], who, however, believed in astrology even more than in signatures. He says: “it is of great use with many physicians to help the diseases of the lungs and for coughs, wheesings and shortness of breath which it cureth both in man and beast.” He adds that “Jupiter seems to own the herb.” A century later we find Dr John Hill[1276], who was a physician as well as a naturalist, stating that the great tree lung-wort has been at all times famous in diseases of the breast and lungs, but by that time “it was not much used owing to change in fashions.”
The only lichen that has stood the test of time and experience as a real remedy is Cetraria islandica, and even the “Iceland moss” is now rarely prescribed. The first mention in literature of this famous plant occurs in Cordus[1277] as the Muscus with crisp leaves. Some years later it figures among the medicinal plants in Sibbald’s[1278] Chronicle of the Scottish Flora, and Ray[1279] wrote of it about the same time as being known for its curative and alimentary properties. It was Linnaeus[1280], and later Scopoli[1281], who gave it the important place it held so long in medicine. It has been used with advantage in many chronic affections as an emollient and tonic. Cramer[1282] in a lengthy dissertation gathered together the facts pertaining to its use as a food, a medicine and for dyeing, and he gives recipes he had himself prescribed with marked success in many different maladies. It has been said that if “Iceland moss” accomplished all the good it was alleged to do, it was indeed a “Divine gift to man.”
The physiological action of cetrarin (acid principle of the lichen) on living creatures has been studied by Kobert[1283] and his pupils. It has not any poisonous effect when injected into the blood, nor does it work any harm when taken into the stomach even of small animals, so that it may be safely given to the most delicate patients. Nearly always after small doses peristaltic movements in the intestines are induced which indicate that as a drug it might be of service in the case of enfeebled organs. In larger doses it may cause collapse in animals, but if administered as free cetraric acid it passes through the stomach unchanged to become slowly and completely dissolved in the intestine. The mucous membrane of the intestine of animals that had been treated with an overdose, was found to be richer in blood so that it seems as if cetrarin might be of service in chlorosis and in assisting digestion.
Cetrarin has also been proved to be a nerve excitant which might be used with advantage in mental maladies.
C. Lichens as Poisons
Though the acid substances of lichens are most of them extremely irritating when taken internally, very few lichens are poisonous. Keegan[1284] writing on this subject considers this quality of comparative innocuousness as a distinctive difference between fungi and lichens and he decides that it proves the latter to be higher organisms from a physiological point of view: “the colouring matters being true products of deassimilation, whereas those of fungi are decomposition or degradation waste products of the albuminoids akin to alkaloids.”
The two outstanding exceptions to this general statement are the two Alpine species Letharia vulpina and Cetraria pinastri. The former contains vulpinic acid in the cortical cells, the crystals of which are lemon-yellow in the mass. Cetraria pinastri produces pinastrinic acid in the hyphae of the medulla and the crystals are a beautiful orange or golden yellow.