1044 ABSORPTION 



quently, ketosis is caused by an imperfect balance between the metab- 

 olism of the fats and carbohydrates.^ 



A term frequently met with in the Hterature upon carbohydrate 

 metabolism is the D:N ratio. We have seen that the absolute with- 

 drawal of carbohydrate from a diabetic animal does not prevent the 

 excretion of sugar in its urine. Since this dextrose is not derived 

 from the fats, it must be synthetized from the proteins. Minkowski 

 and Lusk^ have shown that a dog in complete glucose intolerance may 

 form as much as 60 grm. of glucose. Now, inasmuch as 100 grm. 

 of proteins yield about 16 grm. of nitrogen in the urine, the ratio of 

 dextrose to nitrogen would be 60 : 16 = 3.7. Lusk states that a D :N 

 ratio varying between 3.3 and 3.7 is a fatal ratio, because it proves 

 that a person kept on a diet which is free from carbohydrate, cannot 

 consume sugar. 



THE METABOLISM OF THE FATS 



The Source of the Body Fat. — The neutral fats formed by a resyn- 

 thesis of the fatty acid and glycerin in the lining cells of the intestine, 

 find their way into the lacteals, whence they reach the blood stream 

 by way of the thoracic duct. But since the fat content of the blood 

 of the portal vein is invariably higher than that of the external jugular, 

 it is claimed by some investigators that a slight amount of fat also 

 enters the intestinal capillaries directly. As far as the systemic blood 

 is concerned, it has been found that its content in fat (0.7 per cent.) 

 remains tolerably constant, provided only moderate amounts of fat 

 are ingested. The intake of larger quantities of fat, on the other hand, 

 invariably raises its percentage, which reaches its maximal value about 

 6 hours after a meal and then gradually declines to the twelfth hour. 

 But since even the intravenous injection of oil emulsions does not last- 

 ingly increase the fat content of the blood, it must be concluded that 

 the body possesses the power of storing this fat very rapidly, possibly 

 in the liver. Even during starvation the blood-fat remains rather 

 constant, proving thereby that the fat is being transported from the 

 different depots to the starving tissues. 



In the animal body the fats are usually deposited as the triglyc- 

 erides of the different fatty acids, those of adipose tissue consisting 

 of stearic, palmitic and oleic acids. Cow's milk also contains these 

 acids, but in addition, also the esters of butyric and caproic acids and 

 small amounts of caprylic, capric, lauric and myristic acids. Lard 

 is made up in considerable part of the glycerides of the more unsatu- 

 rated fatty acids, such as those of linoleic acid. It is evident, therefore, 

 that the composition of the fat differs even in one and the same animal, 

 and may in addition be varied by changing the food. This fact proves 

 first of all that the epithelial cells of the intestine do not merely resynthe- 

 tize the glycerol and fatty acids, but possess the power of forming their 



^ Woodyatt, Jour. Am. Med. Assoc, Ixvi, 1916. 

 2 Science of Nutrition, W. B. Saunders Co., 1912. 



