34$ ESSENTIALS OF PHYSIOLOGY. 



be converted into urea, and in acidosis the amount of ammonia excreted 

 in the urine is increased. By this means the acids are neutralised 

 and the reaction of the blood remains unchanged ; and the amount of 

 ammonia in the urine serves as an index of the extent to which these 

 acids are being formed in the body. 



Test for Acetone in Urine. A few c.c. of urine are saturated with ammonium 

 sulphate, and a few drops of ammonia are added ; on the addition of a drop or 

 two of a freshly prepared solution of sodium nitro-prusside a beautiful purple 

 is slowly produced, which varies in depth with the amount of acetone present 

 and fades after a short time. No other substance gives this test, which is 

 called Rothera's test. 



Test for Diacetic Acid in Urine. On adding a solution of ferric chloride, in 

 excess of that required to precipitate the phosphates, the appearance of a deep 

 red colour indicates the presence of diacetic acid. 



There is no simple test for )8-oxybutyric acid. 



Since carbohydrate is readily converted into fat in the body, it 

 might be expected that the converse change would also occur. There 

 is no definite evidence, however, that fat is converted into carbohydrate, 

 except perhaps in hibernating animals, in which the respiratory quotient 

 is extremely low and may be O3 or 0*4. 



Such a quotient could occur if fat were being transformed into 

 dextrose, since, in this process, oxygen would be taken into the body 

 which would not reappear as carbonic acid. 



SECTION III. 



METABOLISM OF CAEBOHYDEATE. 



The carbohydrates are absorbed from the digestive tract and enter 

 the blood stream mainly as dextrose, and to a small extent as fructose 

 and galactose. The arterial blood, when examined, is found to contain 

 O'l to 0'2 per cent, of dextrose, and this amount is not increased after 

 a carbohydrate meal, even though in such circumstances 100 grams 

 or more of sugar may be rapidly absorbed from the digestive tract into 

 the portal blood. The sugar in the portal blood, however, does vary in 

 amount, being slightly less than that in the general circulation during 

 starvation, and distinctly greater after a carbohydrate meal ; and it 

 is clear that the sugar absorbed during digestion undergoes some 

 change as the blood passes through the liver. This change consists in 

 the conversion of sugar into glycogen, which is stored in the liver cells. 



Preparation of Glycogen. An animal is killed a few hours after 

 a meal rich in carbohydrate, and the liver is rapidly excised, chopped 

 into small pieces, and thrown into boiling water. After two or three 

 minutes the pieces of liver are taken out of the water, ground up with 



