794 PHYSIOLOGY 



A further change is the complete oxidation of the last two groups and the 

 production of butyric acid : 



CH 3 .CH 2 .CH 2 .COOH 



This then undergoes again oxidation in the (3 position, with the production 

 of (3-oxybutyric acid : 



CH 3 .CHOH.CH 2 .COOH 



and then again is converted to diacetic acid, 



CH 3 .CO.CH 2 .COOH 



In the normal individual this last stage undergoes complete oxidation, 

 both oxybutyric acid and diacetic acid given to a healthy person being 

 completely destroyed in the body. It is only under the abnormal conditions 

 which we have mentioned above that these last stages fail of complete 

 oxidation, and are excreted unchanged in the urine. 



THE QUESTION OF THE FORMATION OF SUGAR FROM FAT 

 The ease with which the animal body performs the difficult chemical 

 operation of transforming carbohydrate into fat suggests that under 

 appropriate conditions it might effect the reverse change. Is there any 

 evidence that in the animal body sugar may be derived from fat ? Such 

 a conversion is of normal occurrence during the germination of fatty seeds, 

 starch sugar and cellulose being formed at the expense of the stored-up 

 fats of the seeds. If such seeds be allowed to germinate over mercury in 

 a confined volume of oxygen, they are found, like seeds containing chiefly 

 carbohydrate reserves, to absorb oxygen and to give off carbon dioxide. 

 Whereas, however, in the latter case the amount of carbon dioxide evolved 

 is almost equal to the oxygen absorbed, in the case of the fatty seeds much 

 less 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 hibernation, 

 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 appreciable increase in 

 the weight of the animal, which under such circumstances is literally living 

 on air. This retention of oxygen can only be explained by assuming that 

 there is a conversion of substances 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 hibernation 

 indicate the reverse change of fat into carbohydrate. 



The same conversion has been alleged to take place in certain cases of 



