68 CHEMICAL PHYSIOLOGY. 



escent filtrate is an imperfect solution of glycogen (Briicke's 

 method). 



(c.) Instead of a rat or rabbit's liver, use oysters, and pre- 

 pare a solution of glycogen by methods (a.) or (b.) 



(d.} Use the other half of the liver of the rat or rabbit 

 that has been kept warm, and make a similar extract of it. 



2. Precipitate the Glycogen. Evaporate the nitrate of (a.) or (b. ) 

 to a small bulk, and precipitate the glycogen as a white powder 

 by adding a large amount of alcohol. 



3. Preparation of Potassio-mercuric Iodide. Precipitate a 

 saturated solution of potassic iodide with a similar solution of 

 mercuric chloride ; wash the precipitate, and dissolve it to satura- 

 tion in a hot solution of potassic iodide. 



4. Tests. 



(a.) To the opalescent nitrate add a solution of iodine= 

 a port-wine red colour (like that produced by dextrin). If 

 much glycogen be present the colour disappears, and more 

 iodine has to be added. Heat the red fluid ; the colour dis- 

 appears on heating, but reappears on cooling. 



N.B. In performing this test, make a control-experiment. 

 Take two test-tubes, A and B. To A add solution of glycogen ; 

 to B, an equal volume of water. To both add the same amount 

 of iodine solution. A becomes red, while B is but faint yellow. 



(b.) Test a portion of the glycogen solution for grape- 

 sugar. There should be none, or only the faintest trace. 



(c.) To a portion of the glycogen solution add saliva or 

 Liquor Pancreaticus (A), and to another portion add blood 

 (B), and place both on a water-bath at 40 C. After ten 

 minutes test both for sugar. (A) will now be transparent, 

 and give no reaction with iodine. Perhaps both will give 

 the reaction ; but certainly (A) will, if care be taken that the 

 solution is not acid, after adding the saliva. The ptyalin 

 converts the glycogen into a reducing sugar. 



(d.) Boil some glycogen solution with dilute hydrochloric 



