CHAPTER VII. 

 INTERNAL SECRETIONS. 



I. LIVER, GLYCOGEN. 



i. SELECT a well-nourished rabbit. Kill quickly by a sudden 

 blow upon the back of the neck in the region of the medulla. As 

 speedily as possible, open the abdomen and remove a portion of the 

 liver. Cut this into small pieces. Place some of these pieces in boil- 

 ing water; and place one piece immediately on the holder of a 

 freezing microtome and freeze the piece. 



(a) Make a number of sections with the freezing microtome, and 

 as soon as cut place in Lugol's solution containing iodine and po- 

 tassium iodide. Allow the sections to remain in the staining solu- 

 tion for two or three minutes. Wash in water to remove excess of 

 the iodine solution. Mount in glycerin and examine under the 

 microscope. 



The glycogen present in the liver cells will be stained a mahog- 

 any red by the iodine. Compare this reaction with that given by 

 dextrin with iodine. 



(b) Allow some of the rabbit's liver to remain in the incubator 

 at body temperature for an hour or longer. Cut frozen sections of 

 a piece of this and treat with iodine as before. Is there any gly- 

 cogen reaction ? 



(c) Grind some of the incubated liver with sand in a mortar. 

 Add two or three volumes of water. Allow to stand for several 

 minutes. Strain through muslin and filter through paper, and test 

 for reducing sugar with Fehling's solution. 



(d) To prepare glycogen, take the pieces of liver which have 

 been immersed in the boiling water, grind them in a mortar with 



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