406 



ECONOMIC AND TECHNICAL 



Cetraria islandica and some other lichens as foreign drugs. Dr Schweinfurth 

 considered his discovery important as proving the use of foreign remedies 

 by the ancient Egyptians. 



b. DOCTRINE OF "SIGNATURES." In the fifteenth century A.D. there was 

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

 guidance of nature. It was believed that Providence had scattered here 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 Ach. (S H., 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 pulmonaria, the 

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

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

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

 is dotted with small wart-like tubercles 1 , was recommended for children who 

 suffered from the "thrush" eruption. 



1 See p. 138. 



