888 PHYSIOLOGY 



fat of the food it tends to be of the more fluid acids and contains a 

 larger percentage of olein. 



Although it is impossible to trace out all the steps in the process 

 of conversion of sugar into fatty acid, we are acquainted with certain 

 reactions which may throw some light on the nature of the changes 

 involved. If we compare the formula of dextrose with that of the 

 corresponding fatty acid, caproic acid, 



CH 3 CH 2 OH 



CH 2 CHOH 



OH 2 CHOH 



CH 2 CHOH 



CH 2 CHOH 



COOH CHO 



we see that the conversion involves a considerable loss of oxygen. In 

 order to convert three molecules of glucose, C 6 H 12 6 , into one molecule 

 of stearic acid, C 18 H 36 2 , it is necessary to split off 16 atoms of oxygen. 

 That this setting free of oxygen actually occurs in the transformation 

 of carbohydrate into fat is shown by the study of the respiratory 

 exchanges of animals which are rapidly laying on a store of fat at 

 the expense of a carbohydrate food. Thus the marmot, towards the 

 end of summer, eats large quantities of carbohydrate food and very 

 rapidly lays on a thick layer of subcutaneous fat to last it during the 

 winter. If glucose were entirely oxidised in the body the amount of 

 oxygen absorbed would be exactly equal to the amount of carbon 

 dioxide evolved. Thus C 2 H 12 6 + 60 2 = 6C0 2 + 6H 2 0. 

 In this case the respiratory quotient would be 



6C0 9 



60. 



= 1 



If, however, oxygen is being set free by the conversion of part of 

 the carbohydrate into fat, this oxygen will be available for the oxida- 

 tion of other portions of the carbohydrate. The animal will not need 

 to take in so much oxygen from outside for the production of the same 

 amount of carbon dioxide, and the carbon dioxide output of the animal 

 will therefore be greater than its oxygen intake. Pembrey has shown 

 that under these conditions the respiratory quotient may be as high as 

 1*5. We cannot assume, however, that the process of conversion of 

 glucose into fatty acids takes place by this simple process of deoxidation. 



