IX. PHARMACOLOGY 313 



tent of the brain is so low. The essential fatty acids are capable of destroying 

 the chemical carcinogens 3,4-benzopyrene''^ and 20-methylcholanthrene by 

 a coupled oxidation, but 1 ,2,5,6-dibenzanthracene is destroyed much more 

 slowly.-- Linoleic and arachidonic acids^'' also destroy N , N-dimethylamino- 

 azobenzene. Linseed oil and lard have no effect on actions of carcinogens 

 incorporated in these lipids. ^^ 



The RQ of isolated rat liver is increased to 1.23 by linolenic acid, and to 

 0.95 by a mixture of oleic and linoleic acids, although both the latter acids 

 decrease it when added singly .^^ 



B. BIOLOGICAL ASPECTS 



Considerable progress has been made in the study of the normal role of 

 the essential fatty acids in microorganisms, plants, and animals. Linoleic 

 acid is a growth stimulant for some species of Lactobacillus,'^^ • ^^ but not for 

 others.-^'-^ Linoleic, linolenic, and arachidonic acids are essential to growth 

 of an unidentified Micrococcus,^^ and enhance growth of others,^" whereas 

 the saturated acids are ineffective. Linoleic acid is essential for sustained 

 growth in vitro of Trichomonas vaginalis}^ 



A possible relation of linolenic acid content to longevity and germination 

 of pine seeds is suggested^- through parallel species variation. 



The biological importance of variation in linoleic acid content of plants 

 used as food by insects is noted^^ in regard to the sugar beet webworm, 

 Loxostege sticlicalis L. Sterile females of this species are also abnormal in 

 that they contain no linoleic acid; of their host plants, lamb's quarters con- 

 tain 20.5 % and sugar beets or sage less than 1 % of linoleic acid, in terms of 

 total fatty acids, suggesting the significance of diet in sterility in this species. 

 Ephestia spp., Tenebrio molitor, and various beetles and moths have been 



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