608 A MANUAL OF PHYSIOLOGY 



the continued metabolism of the tissues for some time after the 

 heart has ceased^to beat, for the cell dies harder than the body. 

 (2) In the diminished loss of heat, due to the stoppage of the 

 circulation. (3) To a small extent in physical changes (rigor 

 mortis, coagulation of blood) in which heat is set free. 



PRACTICAL EXERCISES ON CHAPTERS VII. AND VIII. 



i. Glycogen* (i) Preparation. (a] Cut an oyster into two or 

 three pieces, throw it into boiling water, and boil for a minute or two. 

 Rub up in a mortar with clean sand, and again boil. Filter. 

 Precipitate any proteins which have not been coagulated, by adding 

 alternately a drop or two of hydrochloric acid and a few drops of 

 potassio-mercuric iodide so long as a precipitate is produced. Only 

 a small quantity of these reagents will be required, as the greater 

 part of the proteins has been already coagulated by boiling. Filter 

 if any precipitate has formed. The nitrate is opalescent. Precipi- 

 tate the glycogen from the nitrate (after concentration on the 

 water-bath if it exceeds a few c.c. in bulk) by the addition of four 

 or five times its volume of alcohol. Filter off the precipitate, wash it 

 on the filter with alcohol, and dissolve it in a little water. To some 

 of the solution add a drop or two of iodine ; a reddish-brown (port 

 wine) colour is produced, which disappears on heating, returns on 

 cooling, is removed by an alkali, restored by an acid. Add saliva 

 to some of the glycogen solution, and put in a bath at 40 C. In a 

 few minutes reducing sugar (maltose) will be found in it by Trommer's 

 test (p. 10). 



Note that dextrin (erythrodextrin) gives the same colour with 

 iodine as glycogen does. Dextrin is also precipitated by alcohol, 

 but a greater proportion must be added to cause complete precipita- 

 tion. Glycogen is completely precipitated by saturation with mag- 

 nesium sulphate or ammonium sulphate, so that the filtrate no longer 

 gives the reddish colour with iodine. A pure solution of erythro- 

 dextrin is not precipitated. On the addition of a drop or two of 

 a solution of basic lead acetate to a solution of glycogen in distilled 

 water, a precipitate forms immediately. When the same reagent 

 is added to a solution of dextrin in distilled water there is no 

 immediate precipitate. Maltose is formed when dextrin is digested 

 with saliva. 



(b) Cut another oyster into pieces, throw it into boiling water 

 acidulated with dilute acetic acid, and boil for a few minutes. Rub 

 up in a mortar with sand, boil again, and filter. Test a portion of 

 the filtrate with iodine for glycogen. Precipitate the rest with 

 alcohol, filter, dissolve the precipitate in water, and test again for 

 glycogen. On boiling some of the opalescent solution for a few 

 minutes after the addition of a few drops of sulphuric acid the 

 opalescence disappears, and when the solution has been neutralized 

 with sodium hydroxide it gives Trommer's test, owing to the 

 hydrolysis of the glycogen into dextrose. 



* For the quantitative estimation of glycogen in organs, Pfliiger's 

 method is the best. The organ is minced and heated with strong (60 per 

 cent.) potassium hydroxide. The glycogen is precipitated with alcohol, 

 and then, after hydrolysis with hydrochloric acid, estimated as dextrose. 



