THE HISTORY OF FAT IN THE BODY 895 



CO.NH.CH 2 COOH. In each case the fatty side-chain is protected 

 from further oxidation by its attachment to the benzene ring and 

 by the tacking on of the glycine molecule. 



With phenylpropionic acid two carbon atoms of the side-chain 

 are oxidised, and the remaining benzoic acid excreted as hippuric 

 acid. Phenylbutyric acid undergoes a similar change ; two carbon 

 atoms are oxidised away, leaving phenylacetic acid, which is excreted 

 as phenylaceturic acid. 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 condition is found in the acetonuria 

 of acute acidosis, such as occurs in the end stages of diabetes. 

 The oxybutyric and diacetic acids occurring in the urine in this 

 condition were formerly thought to be derived from the carbo- 

 hydrates 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 dipt, 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 disposal 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, oxy- 

 butyric 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 sole source of the ^-oxybutyric acid and the diacetic 

 acid is the fats of the food or of the body. The condition of 



