4o6 



ECONOMIC AND TECHNICAL 



Cetrai la islandica and some other lichens as foreign drugs. Dr Schweinfurth 

 considered his discovery important as proving the use of foreign rer^edies 

 by the ancient Egyptians. i 



b. Doctrine of " Signatures." In the fifteenth century a.d. theje was 

 in the study and treatment of disease a constant attempt to follow the 

 guidance of nature. It was believed that Providence had scattered her^ and 

 there on plants "signatures," or resemblances more or less vague to parts 

 of the human body, or to the diseases to which man is subject, thus indi- 

 cating the appropriate specific. 





Fig. 131. Parmelia saxatilis Kc\i. (S/ii., Photo.). 



Lichens among other plants in which any "signature" could be detected 

 or imagined were therefore constantly prescribed : the long filaments of 

 Usnea barbata were used to strengthen the hair; Lobaria pubnonaria, the 

 true lung-wort, with its pitted reticulate surface (Fig. 72), was marked as a 

 suitable remedy for lung troubles; Xanthoria parietina being a yellow lichen 

 was supposed to cure jaundice, and Peltigera aphthosa, the thallus of which 

 is dotted with small wart-like tubercles^, was recommended for children who 

 suffered from the "thrush" eruption. 



' See p. 138. 



