VIII. EFFECTS OF DEFICIENCY 307 



a. Gross Changes 



Maintenance of young dogs on diets practically devoid of fat (less than 

 1 % of the total calories consumed) resulted in marked changes in the ap- 

 pearance of the animals.^*^ The distinctive abnormalities were dryness of 

 the skin and hair with desquamation, increased susceptibility to infection 

 and later tremulousness, drainage from the auditory canals, swelling and 

 redness of the paws, and emaciation. Animals placed on a low fat diet at 

 weaning began to show skin changes within a period of about 3 months. 

 Improvement varied both with the amount and type of fat fed. When fat 

 was fed to equal 5 % of the total calories, there was little improvement in 

 the appearance of the skin ; at the 10 % level some improvement resulted ; 

 but even at a 15 % level healing was rather prolonged. Lard or bacon 

 drippings as the source of dietary fat were more effective in bringing about 

 restitution of the abnormalities than butter fat, both in relation to time 

 and degree. When the deficient animals were given fat at the 30 % caloric 

 level, improvement was rapid (few weeks) and definite, being more rapid 

 with lard and bacon drippings than with butter fat. One animal was on the 

 low fat diet for as long as 6 years, and it is rather remarkable that, although 

 the skin and hair abnormality had been present for this length of time, 

 when sufficient fat again was added to the diet the skin and hair resumed a 

 healthy appearance. In only a few instances in the studies with dogs was it 

 possible to use linoleic or arachidonic acid as the source of fat. When fed at 

 a 1 % caloric level, however, there was definite improvement in the skin 

 and renewed growth of hair. Nevertheless, it was found that this level was 

 not sufficient to effect complete and permanent cures within a 6-month 

 period. In control animals given the same diet from the time of weaning 

 except for the isocaloric substitution of sucrose with lard, bacon drippings, 

 or butter fat in amounts equal to approximately 30 % of the total calories, 

 no abnormalities developed. Illustrations of the gross appearance of dogs 

 suffering fat deficiency are presented in the discussion by Holman in 

 another portion of this volume. 



b. Tissue Lipids 



Rather extensive studies^^ of the tissue lipids have demonstrated that 

 the degree of unsaturation of the fatty acids of the blood serum, skin, sub- 

 cutaneous fat, liver, kidney, and heart is definitely decreased in the animals 

 on the low fat regimen. In general, the differences in the iodine number of 

 the fatty acids between healthy control animals and fat-deficient animals 

 are much greater in the serum than in the skin or other tissues. The iodine 

 number of the serum fatty acids which are particularly involved have been 

 those present as cholesterol ester. Direct correlations have been observed 

 between the appearance of the skin and hair of the animals and the iodine 



