XII.] GLYCOGEN IN THE LIVER. 93 



must be added. Filter; wash the precipitate on the filter with 

 absolute alcohol and ether, and dry it over sulphuric acid or in a 

 hot-air oven (fig. 47). 



3. Preparation of Potassio-Mercuric Iodide or Brucke's Reagent. Pre- 

 cipitate a saturated solution of potassic iodide with a similar solution of 

 mercuric chloride ; wash the precipitate, and dissolve it to saturation in a hot" 

 solution of potassic iodide. 



4. Tests for Grlycogen. 



(<7.) To the opalescent filtrate add iodine solution = a port wine 

 red or mahogany-brown colour (like that produced by dextrin). 

 If much glycogen be present the colour disappears, and more iodine 

 has to be added. Heat the fluid; the colour disappears, but re- 

 appears on cooling. 



N.B. In performing this test, make & control-experiment. Take two test- 

 tubes, A and B. In A place glycogen solution ; in B, an equal volume of 

 water. To both add the same amount of iodine solution. A becomes red, 

 while B is faint yellow. 



(/>.) To another portion add lead acetate = a precipitate (unlike 

 dextrin). The solution must be free from proteids and mercuric 

 salts. 



('.) To another portion add lead acetate and ammonia ; the 

 glycogen is precipitated (like dextrin). 



(d. ) Test a portion of the glycogen solution for grape sugar. There may be 

 none, or only the faintest trace. 



(e.) To a portion (A) of the glycogen solution add saliva or liquor 

 pancreaticus, and to another portion (B) add blood, and place both in a 

 water bath at 40 C. After ten minutes test both for sugar. (A) will be 

 transparent, and give no reaction with iodine. Perhaps both will give the 

 sugar 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. 



(/.) Boil some glycogen solution with dilute hydrochloric acid in a flask ; 

 neutralise with caustic soda, and test with Fehl ing's solution for sugar. 



5. Test the watery extract of the other half of the liver. 

 (a.) Perhaps no glycogen reaction, or only a slight one. 

 (A.) It contains much reducing sugar. 



6. Extract of a Dead Liver. 



(a.) Mince a piece of liver from an animal which has been dead 

 for 24 hours. Boil the liver either in water or a saturated solution 

 of sodic sulphate. Filter ; the filtrate is clear and yellowish ID 

 tint, but not opalescent. 



(6.) Its reaction is acid to litmus paper. 



