ECONOMIC USES OF LICHENS — LLANO 403 



cies of Cladonia inhibited. B. subtilis but not S. aureus. Extracts from 

 Cladonia furcata Schrad., CI. j^cipillaiia Hoff., and TJ inhUicaiia papu- 

 losa inhibited S. aureus but were inactive against B. subtilis. Further- 

 more, the inhibition of some Gram-negative bacteria by selected species 

 of lichens lends further support to the theory of multiple substances. 

 The authors pose the question : Do the characteristic lichen acids pos- 

 sess antibacterial activity or are the antibiotic properties of lichens 

 related to traces of other unidentified substances synthesized by these 

 plants? Burkliolder and his associates noted that some of the lichen 

 compounds possess certain structural features in common with antibac- 

 terial substances isolated from molds, but they could not be sure that 

 these were responsible for the antibiotic phenomena observed. They 

 point out the fact that "almost nothing is known about the anabolism 

 of the components or the roles of the various substances formed in the 

 lichen body." In a subsequent report, Burkliolder and Evans (3) reach 

 the conclusion that "the phenomenon of antibiosis ... is well exem- 

 plified in the lichens." These antibiotic substances are apparentl}^ dif- 

 ferent from penicillin, for the activity of several species of lichens w^as 

 not lost after boiling in NaaCOs solution. Samples of lichens collected 

 from different regions showed, on the whole, characteristic activity in 

 antibiotic tests with suitable bacteria. No explanation is offered for 

 the variability, though there may be some relationship between tliis 

 phenomenon and the fact that some of the diagnostic lichen acids vary 

 in different samples of some lichen species. Though diagnostic com- 

 pounds known to occur in the antibiotic species of Cladonia are listed, 

 the authors suggest that other unidentified substances might be re- 

 sponsible for the observed antibacterial properties. The presence of 

 antibacterial substances in numerous species of Cladonia and in rep- 

 resentatives of other genera of lichens appears to be definite, but 

 whether these are bacteriocidal or merely bacteriostatic is not proved. 

 Although Gram-positive bacteria, including several pathogenic types, 

 are inhibited. Gram-negative bacteria, with a few exceptions, are 

 generally not susceptible to the antibiotic substances of lichens. 



Other research (la) on antitubercular compounds indicates another 

 promising possibility for a lichen compound. Numerous acids were 

 the subject of synthetical studies by various workers in the field of 

 antitubercular compounds. Barry began with roccellic acid isolated 

 from Lecanora sordida Th. Fr. The author states : "We have already 

 reported that this substance in the form of its half-esters or half- 

 amides inhibits completely the growth of the tubercle bacillus in vitro 

 at a dilution of about one five-hundred-thousandths." Barry adds 

 that "the most active of these compounds are at the moment being 

 tested in animal-protection experiments, and although they are 

 strongly antagonized by serum in vitro, they seem to have some activ- 

 ity in the animal." 



