8 TEXT-BOOK OF PHYSIOLOGY. 



Glycogen is a constituent of the animal liver, and, to a slight extent, 

 of muscles, 0.5 to 0.9 per cent., and of tissues generally. In the tissues of the 

 embryo it is especially abundant. When obtained in a pure state it is an 

 amorphous, white powder. It is soluble in water, forming an opales- 

 cent solution. With iodin it strikes a port-wine color. In some respects 

 it resembles starch, in others dextrin. Like vegetable starch, glycogen or 

 animal starch can be converted by dilute acids and ferments into sugar 

 (dextrose). 



Cellulose is the basic material of the more or less solid framework 

 of plants. It is soluble in ammoniacal solution of cupric oxid, from which 

 it can be precipitated by acids. It is an amorphous powder; dilute acids can 

 convert it into dextrose. 



2. DEXTROSES, C 6 H 12 O e . 



Dextrose, glucose, or grape-sugar is found in grapes, most sweet 

 fruits, and honey, and as a normal constituent of liver, blood, muscles, 

 and other animal tissues. In the disease diabetes mellitus it is found also 

 in the urine. 



When obtained from any source, it is soluble in water and in hot alcohol, 

 from which it crystallizes in six-sided tables or prisms. As usually met with, 

 it is in the form of irregular, warty masses. It is sweet to the taste. When 

 examined with the polariscope, it will be found that dextrose turns the plane 

 of polarized light to the right. It is therefore termed dextro-rotatory and 

 has received its name from this fact. 



It has for a long time been known that when sugar, cupric hydroxid, and 

 an alkali e.g., sodium or potassium are present in solution, the sugar 

 will abstract from the cupric hydroxid a portion of its oxygen, thus reducing 

 it to a lower stage of oxidation giving rise to cuprous oxid. Sugar has a 

 similar action on both silver and bismuth. On this property of sugar a 

 standard solution of cupric hydroxid was suggested by Fehling which may 

 be employed for both qualitative and quantitative tests for the presence of 

 sugar in solution. 



Fehling's Test Solution. This is a solution of cupric hydroxid made 

 alkaline by an excess of sodium or potassium hydroxid with the addition 

 of sodium and potassium tartrate. It is made by dissolving cupric sulphate 

 34.64 grams, potassium hydroxid 125 grams, sodium and potassium tartrate 

 173 grams, in distilled water sufficient to make one liter. 

 The reaction is expressed by the following equation : 



The object of the sodium and potassium tartrate is to dissolve the cupric 

 hydroxid and hold it in solution. 



For qualitative analysis it is only necessary to boil a few cubic centi- 

 meters of this solution in a test-tube; then add the suspected solution and 

 again heat to the boiling-point. If sugar be present, the cupric hydroxid 

 is reduced to the condition of a cuprous oxid, which shows itself as a red 

 or orange-yellow precipitate. The color of the precipitate depends on the 

 relative excess of either copper or sugar, being red with the former, orange 

 or yellow with the latter. The delicacy of this test is shown by the fact that 

 a few minims of this solution will detect in i c.c. of water the T V of a milli- 

 gram of sugar. (Dextrose.) 



