836 PHYSIOLOGY 



If phenyl valerianic acid be given, four carbon atoms are oxidised away 

 and benzoic acid is left, and appears in the urine as hippuric acid. In 

 each case the oxidation of the side-chain occurs by two carbon atoms at 

 a time, and it seems probable that a similar change will occur in the ordinary 

 fatty acid, the last stages, in the absence of any protective ring compound, 

 being oxidised like the earlier groups and therefore not detectable in the 

 excretions. 



Evidence in the same direction is afforded by certain cases in which 

 the oxidative power of the body for fats is inadequate, either by reason of 

 morbid changes in the oxidative powers of the body, or as the result of 

 what we may call an overstrain, of the fat-oxidising powers. Such a con- 

 dition is found in the acetonuria of acute acidosis, such as occurs in the 

 end stages of diabetes. The oxy butyric and diacetic acids occurring in 

 the urine in this condition were formerly thought to be derived from the 

 carbohydrates of the food, or from sugar abnormally produced in the 

 body. The condition of acidosis however is often brought on directly 

 as the result of putting the patient on a strict anti-diabetic diet, i. e. one 

 consisting chiefly or exclusively of fats and proteins, and may be produced 

 in a healthy man by simple starvation, when the body has only at its dis- 

 posal its stored-up fats and proteins. It occurs in a marked degree on 

 the administration of a diet consisting almost entirely of fats. . Thus in 

 one experiment a healthy man took as his sole diet for five days a daily 

 ration of 250 grm. of butter, 200 grm. of oil, and a little wine. The result 

 was an intense acidosis, such as is only found in the severest cases of 

 diabetes, diacetic acid, oxybutyric acid, and acetone being found in the 

 urine in large quantities. On the last day of the experiment these acids 

 caused so much of the nitrogen in the urine to appear as ammonia that of 

 the 5-8 grm. total nitrogen excreted only 2-7 grm. were in the form of urea, 

 while as much as 2*1 grm. were present as ammonia. 



If, during a period of starvation in man, a day is interpolated on which 

 100 grm. of protein are taken, the amount of acetone excreted falls below 

 that obtained on the other days when the individual is living chiefly at 

 the cost of his own fat. These facts indicate that the chief source of the 

 /ft-oxybutyric acid and the diacetic acid is the fat of the food or of the 

 body. The condition of acidosis is more easily brought about by ingestion 

 of butyric acid than of the higher acids, such as palmitic or stearic, sug- 

 gesting that whatever fatty acid is given it is finally reduced to butyric 

 acid before its oxidation, and that in the condition of acidosis it is merely 

 the last stages of this oxidation which are at fault. We are thus justified 

 in concluding that the oxidative breakdown of fats occurs always by an 

 oxidation in the ft position. 



We take, for instance, the 6-carbon stage : 



CH 3 .CH 2 .CH 2 .CH 2 .CH 2 .COOH 



the first change which probably occurs is the oxidation : 

 CH 3 .CH 2 .CH 2 .CHOH.CH 2 .COOH 



