THE HISTORY OF FAT IN THE BODY 897 



carbon dioxide is given out than would correspond to the volume 

 of oxygen absorbed, so that the total volume of gas above the seeds 

 diminishes. 



The same change in the relation of oxygen intake to carbon dioxide 

 output is found under certain conditions in animals. During hiberna- 

 tion, as Pembrey has shown, the marmot has a very low respiratory 

 quotient, which may be not greater than 0-3 or 04. This means that 

 the animal takes in more oxygen than the carbon dioxide which it gives 

 out, and this intake of oxygen can be so marked as to cause an appre- 

 ciable increase in the weight of the animal, which under such cir- 

 cumstances is literally living on air. This retention of oxygen can 

 only be explained by assuming that there is a conversion of sub- 

 stances containing a small amount of oxygen into substances containing 

 a larger amount of oxygen going on in the body, such a conversion 

 as that of fats into carbohydrates. Just as the high respiratory 

 quotient obtained from a marmot during the period of putting on 

 fat was shown to be associated with a conversion of carbohydrate 

 into fat, so does the abnormally low quotient obtained during hiber- 

 nation indicate the reverse change of fat into carbohydrate. 



The same conversion has been alleged to take place in certain 

 cases of diabetes. In many cases when the diabetic animal is living 

 on a purely protein diet, a uniform ratio has been found to exist 

 between the glucose or dextrose and the nitrogen excreted. 



^ equals generally 2-8. 



In certain other cases a constant D : N ratio of 3 -65 has been found. 

 The former represents a conversion of 45 per cent., the latter of 

 58 per cent., of protein into sugar. In a few cases, however, even 

 during complete starvation, the ratio D : N has been found to be much 

 greater than that given above and to amount to as much as 10 or 12. 

 These animals are stated to be practically free from carbohydrates, so 

 that the sugar excreted in the urine can only come from the breakdown 

 of proteins or fats. It is impossible by any means whatever to break 

 up a protein molecule so as to get from it ten times as much dextrose 

 as corresponds to the nitrogen, and Pfliiger concludes that in cases 

 where such a high D : N ratio exists the dextrose must have been 

 derived by a conversion of the fats of the body. This conclusion 

 is by no means generally accepted. If correct, it would bear out 

 the general statement made above, namely, that in the living body 

 practically all the chemical changes are reversible, and that the 

 living cell can so regulate the conditions of the reaction that the 

 reversible reaction becomes practically complete in either direction, 

 the direction being determined by the needs of the body at the time. 



57 



