8 TEXT-BOOK OF PHYSIOLOGY 



Dextrin is a substance formed as an intermediate product in the trans- 

 formation of starch into sugar (maltose). There are at least two principal 

 varieties erythrodextrin, which strikes a red color with iodin, and achroodex- 

 trin, which is without color when treated with this reagent. In the pure 

 state dextrin is a yellow- white powder, soluble in water. In the presence 

 of animal ferments erythrodextrin is converted into maltose. 



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. Cellulose is 

 very stable toward dilute acids and alkalies. It is this property which is 

 made use of in the technical preparation of cellulose, in order to free it from 

 the other substances present in the plant material. When cellulose is 

 treated with strong sulphuric acid, and after disintegration diluted with 

 water and then boiled, it is completely hydrolyzed to dextrose. 



2. DEXTROSES, C 8 H 13 O,. 



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 hydroxid are present in solution, the 

 sugar will abstract from the cupric hydroxid a portion of its oxygen, thus re- 

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

 a similar action on both silver and bismuth salts. 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 



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



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



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



The reaction is expressed by the following equation:' 



