METABOLISM 211 



be excreted when the glycogen supplies of the body have been 

 exhausted. If protein is fed to such an animal, the amount of 

 glucose in the urine increases. There is a certain parallelism 

 between the amount of glucose (dextrose) excreted and the 

 amount of nitrogen in the urine. This is known as the D : N 

 ratio. All the protein is not converted into glucose. Portions 

 of some of the amin'o acids are destroyed or converted into other 

 substances. Sixty grams of glucose is considered the maximum 

 amount which the body can produce from 100 grams of protein 

 (this contains ca. 16 grams nitrogen). A ratio of D : N=60 : 16 

 or about 3.7 :1 would indicate that none of the glucose produced 

 from protein was being burned by the body, in other words a 

 complete failure on the part of the tissues to burn glucose. 3.7 

 is thus known as the fatal ratio. It must be observed, however, 

 when the animal is on a carbohydrate free diet, as otherwise the 

 ratio may, of course, be still higher. By observing the D-N ratio 

 when various amino acids were fed, it has been shown beyond 

 doubt that some amino acids are converted completely into glu- 

 cose in the body, some others only partially. There is thus no 

 question of the formation of glucose (and glycogen) from the 

 carbon chain of the amino acids, and thus indirectly from the 

 proteins. 



Very little glycogen is formed from fat. The glycerine por- 

 tion may be converted into glucose but the fatty acids do not 

 appear to be converted into glucose. 



Metabolism of Fats. The fats are digested in the alimen- 

 tary tract and absorbed in the form of fatty acids and soaps. In 

 this process the bile salts, play an important role. In the cells 

 of the villi, however, a re-synthesis of neutral fat takes place, 

 and at least most of the fatty acids and glycerine are recombined, 

 and poured into the blood stream by way of the thoracic duct. 

 Fats are stored away in a variety of places, subcutaneously, in 

 the intramuscular spaces, around the abdominal viscera and 

 elsewhere. There is practically no limit to the amount which 

 may be laid away. This is in sharp contrast to the non-storage 

 of excess protein, and to the limited glycogen reserves. Fat is 



