PHYSIOLOGICAL CHEMISTRY 291 



gum is dextrine produced by heating starch to 200* C. This sub- 

 stance is much employed as the adhesive substance on stamps and 

 envelopes. There are several varieties of dextrine, varying from one 

 another in molecular weight. The highest dextrine is called amylo- 

 dextrine, the next erythrodextrine, then achroodextrine. 



Dextrine is an amorphous powder, soluble in cold water, and forming 

 a clear solution with which the following reactions can be obtained : 



EXPERIMENT XI. Add some iodine solution ; a brownish red 

 colour, like that obtained with glycogen, results, which disappears on 

 heating and returns on cooling. It is only one form of dextrine 

 erythrodextrine which gives the reaction ; achroodextrine gives no 

 reaction with iodine. The bluish tint sometimes obtained is due to 

 the presence of starch. 



EXPERIMENT XII. Try Trommer's test: no reduction is obtained, 

 but Cu(OH) 2 is held in solution. 



EXPERIMENT XIII. Hydrolyse some dextrine solution and then apply 

 Trommer's test : reduction occurs. 



The Quantitative Estimation of Glycogen in Animal Tissues. 



The importance of a rapid and accurate determination of the amount of 

 glycogen in animal tissues has led to the publication of many different 

 methods. To within a few years ago, however, none of these has been of 

 sufficient accuracy, the difficulty being to separate the glycogen from protein 

 without losing any of the glycogen. It is to Pfliiger that we owe a method 

 which is unquestionably far superior to any of its predecessors. This method 

 depends on two facts : firstly, that glycogen is not affected by heating it on 

 a water bath with thirty per cent, potassium hydroxide solution, whereas 

 protein under such conditions is destroyed ; and secondly, that by the addition 

 of an equal volume of water to the above solution (which will bring the 

 percentage of potassium hydroxide to fifteen) and the subsequent addition of 

 two volumes of alcohol (96%) all the glycogen is precipitated, whereas practi- 

 cally all of the degradation products of protein remain jn solution. The 

 method is as follows x : 



The liver is cut into small pieces and mixed in an Erlenmeyer flask 

 (Bohemian glass) with 100 c.c. 60% KOH. 2 



1 The following description is for 100 gr. liver, but much less than this 

 amount is sufficient for most purposes. Thus, in the case of a dog, fed on the 

 previous day with bread and meat, 20 gr. liver is a suitable amount, and in 

 the case of a rabbit fed with carrots or other carbohydrate-rich food, 10 gr. is 

 sufficient. In the case of muscle, it is best to take 100 gr., as the percentage of 

 glycogen in this tissue is practically never more than one. 



2 Pfliiger specifies ' Merck A ' KOH, but for most purposes ' KOH pure by 

 alcohol ' is of sufficient purity. The strength is best adjusted by the use of a 

 hydrometer (alkalimeter), the specific gravity of such a solution being 1-438 at 

 15 C. or 44 on the Baume scale. 



