546 



VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



feeding tests were started, and the period over which the diet was consumed 

 averaged sixty-six days. The data are summarized in Table 3. 



Table 3 



The Effect of Diet on the Composition of Male Rats Sacrificed after Receiving 



3000 Calories of the Diet under Study 



High- 

 Lipid Adequate High-fat carbohydrate 



analyzed Control b diet diet c diet c 



Calculated in % dry weight 



Total lipid 16.58 44.80 49.10 36.01 



Neutral fat 8.71 40.56 45.16 32.28 



Essential lipid 7.87 4.24 3.94 3.73 



Calculation in % on water-free, neutral fat-free basis 



Essential lipid 8.62 7.13 7.19 5.51 



Cerebrosides 1.35 2.67 2.55 1.20 



Free cholesterol 0.47 0.25 0.26 0.22 



Cholesterol esters 0.82 0.24 0.26 0.37 



Phospholipid 5.98 3.97 4.12 3.72 



Cephalin 2.73 1.41 1.77 1.49 



Lecithin 2.52 2.04 1.69 1.67 



Sphingomyelin 0.73 0.52 0.66 0.56 



° Adapted from H. H. Williams, H. Galbraith, M. Kaucher, and I. G. Macy, ./. Biol. 

 Chem., 161, 463-474 (1945). 



b Rats sacrificed at 22 days of age. 

 c Rats averaged 88 days of age. 



(3) Piotein as a Source of Body Fat 



It has long been known that the nitrogen-free moiety of protein could be 

 converted to carbohydrate. If one admits the thesis that carbohydrate can 

 be converted to fat, one must likewise accept the hypothesis that protein 

 can be changed to fat, carbohydrate acting as an intermediary product. 

 There is no difference qualitatively between the glucose or glycogen arising 

 in the animal body from protein and that which is formed after sugars or 

 starches are ingested. The experimental proof of the transformation of 

 protein to fat is more difficult than is that for carbohydrate. It has been 

 investigated by the use of balance experiments, by interpretation of the 

 data obtained from experiments on respiratory metabolism, and indirectly 

 by the proof of the conversion of proteins and amino acids to carbohydrate. 



a. Balance Experiments as Proof of the Conversion of Protein to Fat. 

 As early as 1862, Pettenkofer and Voit, 149 ' 150 and later Lawes and Gilbert 104 



149 M. Pettenkofer and C. Voit, Ann, Chem. u. Pharm., 2nd Suppl., 52-70, 361-377 

 (1862). 



150 M. Pettenkofer and C. Voit, Z. Biol., 7, 433-497 (1871). 



