CARBOHYDRATES. 87 



Hydrochloric Acid (HC1). Hydrochloric acid exists in the 

 gastric juice. 



Carbon Dioxid (CO 2 ). This gas exists in many of the 

 fluids, having been absorbed by them from the tissues. It is also 

 present in blood and in expired air. 



CARBOHYDRATES. 



This class is so called because its members contain hydrogen 

 and oxygen in the proportion to form water, united with carbon. 

 All substances, however, which have this composition are not 

 carbohydrates, e. g., acetic acid (C 2 H 3 OOH), nor is it to be inferred 

 that a carbohydrate is a compound in which water is simply joined 

 to carbon ; on the contrary its constitution is quite complex. 



Most of the members of this class which are of physiologic 

 interest contain six atoms of carbon or a multiple of that number, 

 and are, therefore, hexoses. 



Carbohydrates are classified as Monosaccharids or Glucoses, 

 Disaccharids or Saccharoses, and Polysaccharids or Amyloses. 



Monosaccharids or Glucoses. The members of this 

 group have the chemical formula C 6 H 12 O 6 . Those which are of 

 special interest are Dextrose, Levulose, and Galactose. 



Dextrose (glucose, grape-sugar, diabetic sugar) is normally 

 found in the blood, chyle, lymph, and in very small amount in 

 the urine. It occurs in grapes and some other fruits, and also 

 in honey. Dextrose and levulose usually occur together. In the 

 disease known as " diabetes mellitus " the quantity of dextrose in 

 the blood and urine is very much increased. It is a substance of 

 much interest, as it is in the form of dextrose that the carbo- 

 hydrates of the food find their way into the blood. In its pure 

 state dextrose is colorless and readily crystallizes ; it is soluble 

 in cold, more so in hot water. It is dextrorotatory, whence it 

 derives its name. In alkaline solutions dextrose reduces metallic 

 oxids, a property which is made use of in determining its pres- 

 ence and in measuring its quantity. 



Various tests are employed for the detection of dextrose ; 

 among these are Trommer's, the fermentation-test, and Fehling's. 



Trommer's Test. The method of applying this test is as 

 follows : 



If the presence of dextrose in an organ is to be ascertained, this 

 should be cut into small pieces and boiled with water and sulphate 

 of sodium, and the mixture filtered in order to have a clear solu- 

 tion, which is essential. Some of this should be poured into a 

 test-tube, and a few drops of a solution of sulphate of copper 

 added. To this a solution of caustic potash should be added, so 

 as to make the contents of the tube distinctly alkaline. The tube 

 should now be heated, when, if dextrose is present, just before the 



