326 PRACTICAL PHYSIOLOGY 



of the substance in a test tube add several c.c. HC1 and a knife point 

 of orcin, then boil. A reddish blue colour develops (a blue pigment is 

 formed). Extract with amyl alcohol the colour changes from reddish 

 to greenish. Examine with a spectroscope. Bands are found between 

 C and D. The addition of a trace of ferric chloride to the hydrochloric 

 acid renders the test more delicate. 



. Presence of phosphorus may be shown by means of the general test 

 for P. The amount may be estimated by the Neumann wet ash method 

 (see p. 289). 



Purin bodies present may be obtained by hydrolysis with a mineral 

 acid and subsequent treatment as in isolation from muscle extracts. 



Detection of Pentoses in Gums. Hydrolyse gum arabic by heating 

 a solution of it in a waterbath for twenty minutes with 5 per 

 cent. HC1. Arabinose is formed. After neutralising, apply reduc- 

 tion and yeast fermentation tests to portions of the solution. To 

 another portion apply the following characteristic test for pentoses 

 (Tollens). Add phloroglucin (C 6 H 3 (OH) 3 ) in small quantities at a time 

 till no more dissolves to a solution of about 5 c.c. of equal parts of 

 concentrated HC1 and water. Then add a few drops of the arabinose 

 solution and warm until a red colour develops. Examine with the 

 direct vision spectroscope when an absorption band will be seen between 

 D and E lines. By further heating, a precipitate forms which becomes 

 dissolved in amyl alcohol when this is shaken with the solution. The 

 amyl alcoholic solution shows the above spectrum very clearly. Tollens' 

 test can be applied to urine. Repeat this test, using dextrose solution. 



The Quantitative Estimation of Glycogen in Animal Tissues. The 



best method is that of Pfliiger. This method depends on two facts : 

 firstly, that glycogen is not affected by heating it on a waterbath with 

 30 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 15) and the subsequent addition 

 of two volumes of alcohol (96 per cent.) all the glycogen is precipi- 

 tated, whereas practically all of the degradation products of protein 

 remain in 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 per cent. KOH. 2 



The flask is closed with a cork, having a wide glass tube about five 

 feet long passing through it to serve as a reflux condenser, and it is then 

 immersed in a boiling waterbath and left there for three hours, with 

 occasional shaking. (Less time than this suffices to completely destroy 

 the protein of liver.) On removal from the waterbath, the contents 

 of the flask are allowed to cool, and are then thoroughly shaken, with 

 200 c.c. water (thus bringing the percentage of KOH to 15). 800 c.c. 



1 The following description is for 100 gms. 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 gms. liver is a suitable amount, and in 

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

 sufficient. In the case of muscle, it is best to take 100 gms., as the percent- 

 age 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 Beaum< scale. 



