298 ESSENTIAL FATTY ACIDS 



are required to develop fat deficiency in rats. It seems possible that for 

 animals having a cecum, intestinal bacteria may play a role in the syn- 

 thesis of essential fatty acids as well as of many of the water-soluble 

 vitamins. 



6. Insects 



Fat-deficiency phenomena are not limited to vertebrates, for Fraenkel 

 and Blewetf'® were able to develop fat-deficient moths of four species. 

 Feeding fat-free diets during the larval stage prevents proper wing develop- 

 ment in the adult (see Fig. 10). Linoleic and linolenic acids prevent this 

 condition, but docosahexaenoic acid does not. However, the latter does 

 benefit growth. Results with these lower animals again point to the differ- 

 ences between the members of the polyunsaturated fatty acid group. Emer- 



5 6 7 8 



Fig. 10. Response of Ephestia keuhniella wing development to various levels of 

 linoleic acid in the larval diet. 1. Normal wing, 8. Fat-free diet. (From Fraenkel 

 and Blewett.26) 



gence from the pupal stage and scale development of the adult wing paral- 

 lels the linoleic acid content of the diet. It appears that these moths or 

 other insects might be useful and inexpensive animals for essential fatty acid 

 assay. 



As yet studies of the requirements of microorganisms for essential fatty 

 acids have not been made, nor have mutants requiring these acids been 

 isolated. It seems likely, however, that mutants requiring the acids could 

 be produced and isolated for use in the assay of these essential fatty acids. 



7. Histopathology 



In addition to the gross abnormalities of fat-deficient animals mentioned 

 in the previous section, a few observations have been made on the histo- 

 pathology accompanying fat deficiency. Histological examinations of the 

 kidneys of deficient rats"' -^ indicate that the renal tubules are calcified 



26 G. Fraenkel and M. Blewett, /. Exptl. Biol. 22, 172 (1946). 



27 V. G. Borland and C. M. Jackson, Arch. Pathol. 11, 687 (1931). 



28 R. H. Follis, The Pathology of Nutritional Disease. Charles C Thomas, Spring- 

 field, 111., 1948. 



