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-Merciiric Iodide or Briicke'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 Glycogen. 



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

 red or mahogany-brown colour (Hke 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 cooUng. 



A".^.— In performing this test, make a. 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. 



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

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

 salts. 



(f.) 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 ])ortion (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 Fehlings 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. 

 (h.) 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 in 

 tint, but not opalescent. 



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



