548 VI. OCCURRENCE OF LIPIDS IN THE ANIMAL 



days, the animal was fed all the lean meat it would eat over an eight-day 

 period. During this interval, the cat was kept in a respiration chamber, 

 and the total excreta were collected. The carbon present in meat protein 

 was calculated from the urinary nitrogen, using the low figure of 3.2, which 

 is even lower than the ratio (3.28) obtained by Rubner. 151 At the con- 

 clusion of the test, the animal was sacrificed and the total glycogen in the 

 tissues was determined. The essential data for the interpretation of the 

 experiment are given in Table 4 (page 547). 



Since Cremer (see Table 4) was able to account for only 35 g. of glycogen 

 in the tissues of the cat, sacrificed after receiving 3600 g. of lean meat over 

 an eight-day period, and since sufficient carbon was retained from the pro- 

 tein to give rise to 131.5 g. of glycogen, one must conclude that most of the 

 carbon moiety of protein was stored in some form other than carbohydrate. 

 The only possible non-protein component in the tissues other than carbo- 

 hydrate which could account for this amount of carbon is fat. The con- 

 clusion is inescapable, therefore, that protein can be converted to fat in the 

 cat. Since there is nothing particularly different in the metabolic picture 

 of the cat from that of other mammals, one can readily accept this experi- 

 ment as proving a general principle. 



b. Respiration Experiments as Proof of the Conversion of Protein to 

 Fat. Atkinson, Rapport, and Lusk 154 designed an interesting experimental 

 procedure based upon data obtained from respiratory metabolism experi- 

 ments for testing the validity of the hypothesis that protein is convertible 

 to fat. By maintaining the glycogen reserves of an animal at a maximum 

 as a result of a previous carbohydrate meal, these workers provided a con- 

 dition which would be most favorable for determining whether the carbon 

 moiety retained at the height of protein metabolism following a protein meal 

 was in the form of carbohydrate or of fat. If the protein had been com- 

 pletely oxidized, the resultant R.Q. would have been 0.801. On the other 

 hand, if the protein carbon retained had, been in the form of carbohydrate, 

 the stored material removed from the metabolic interchange would have 

 had a potential R.Q. of 1.00; the actual R.Q. observed, therefore, would 

 have been reduced below that for protein (0.801), in proportion to the 

 quantity stored as carbohydrate. 



However, if the carbon retained from protein had been stored as fat, 

 this portion of the protein would have been removed from the metabolic 

 interplay as a material having a potential R.Q. of 0.707. The R.Q. of the 

 remaining portion of protein which would then be metabolized would have 

 been increased over and above 0.801 in proportion to the quantity of re- 



164 H. V. Atkinson, D. Rapport, and G. Lusk, /. Biol. Chem., 53, 155-166 (1922). 



